auditory meatus_ (Fig. 21, 16), is well seen in a side view of
the skull; it is bounded on its inner side by the periotic bones,
posteriorly in part by the exoccipital, and elsewhere mainly by the
quadrate. A large number of canals and passages open into it. On its
inner side opening ventro-anteriorly is the _fenestra ovalis_, opening
ventro-posteriorly the _internal auditory meatus_ (Fig. 23, VIII),
while dorsally there is a wide opening which forms a communication
through the roof of the brain case with the tympanic cavity of the
other side. On its posterior wall is the prominent foramen through
which the facial nerve passes on its way to its final exit from the
skull through the exoccipital; this foramen is bounded by the quadrate,
squamosal, and exoccipital. The opening of the _fenestra ovalis_ is in
the fresh skull occupied by the expanded end of the auditory ossicle,
the _columella_, whose outer end articulates by a concave facet with a
trifid _extracolumellar_ cartilage which reaches the tympanic membrane.
The lower process of this extracolumella passes into a cartilaginous
rod which lies in a canal in the quadrate and is during life continuous
with Meckel’s cartilage within the articular bone of the mandible.
“The columella and extracolumella are together homologous with the
chain of mammalian auditory ossicles.”
_The Lower Jaw_ (Figs. 21, 23, and 24). The mandible consists of two
similar rami, rather closely united at the anterior-median symphysis
with each other. Each ramus consists of six bones.
The _dentary_ (Figs. 23 and 24, 18; Fig. 21, 20) is a long bone that
unites at the symphysis with its fellow to form the point of the
jaw. It bears, along its dorsal edge, about twenty teeth; all but
the posterior four or five of these teeth are in individual sockets;
this may vary somewhat with age. The outer surface of the dentary,
especially towards the symphysis, is covered with numerous, small,
deep pits, while along its inner side, parallel to the row of teeth,
is a row of somewhat larger pits like those noted in the maxilla and
premaxilla. Articulating with the mesial side of the dentary along the
greater part of its length is a flat bone, the _splenial_ (Figs. 23 and
24, 19); between these two bones is a long cavity that makes the ramus
hollow almost to the symphysis. A large foramen, not shown in any of
the figures, leads through the splenial into this cavity.
Articulating with the caudal end of the splenial and forming the
anterior border, as seen from the mesial side, of the large _external
mandibular foramen_ (Fig. 23, 27) is a small bone, the _coronoid_
(Figs. 23 and 24, 23, Fig. 21, 21); it articulates with the splenial
anteriorly, with the supra-angular dorso-caudally, and with the angular
ventrally.
The _supra-angular_ (Figs. 23 and 24, 21, Fig. 21, 18) is an elongated
bone that forms the dorsal border of the external mandibular foramen;
it also forms the lateral edge of the articular surface for the
quadrate. It articulates anteriorly with the splenial, the dentary, and
the coronoid; and posteriorly with the angular and articular.
The _articular_ (Figs. 23 and 24, 22, Fig. 21, 19), which is scarcely
visible in a lateral view, forms most of the surface for articulation
with the quadrate, and sends back the large process so characteristic
of the crocodilian skull. On the dorsal side of this process is a
concavity that looks like another articular surface. Laterally the
articular articulates with the supra-angular; ventrally and posteriorly
with the angular.
The _angular_ (Fig. 23, 20, Fig. 21, 22) forms the ventro-posterior
border of the jaw and of the external mandibular foramen. Its narrow,
posterior end forms a part of the prominent process mentioned in
connection with the articular. Between it and the posterior edge of
the splenial is the _internal mandibular foramen_, which is much
smaller than the external (Fig. 23, 28). Anteriorly the angular
articulates with the dentary, coronoid, and splenial; dorsally with the
supra-angular and the articular.
_The Hyoid_ (Fig. 25). The hyoid being mainly of cartilage is usually
not seen in prepared skeletons. It is thus described by Reynolds:
“The hyoid of the Crocodile consists of a wide flattened plate of
cartilage, the _basilingual plate_ or _body of the hyoid_, and a pair
of _cornua_.
“The _basilingual plate_ (Fig. 25, 1) is rounded anteriorly and marked
by a deep notch posteriorly. The _cornua_ (Fig. 25, 3), which are
attached at a pair of notches near the middle of the outer border of
the basilingual plate, are partly ossified, but their expanded ends are
formed of cartilage. They pass at first backwards and then upwards and
inwards. They are homologous with part of the first branchial arches of
Selachians.”
[Illustration: FIG. 25. HYOIDS OF AN ALLIGATOR (_Caiman latirostris_)
(TO THE LEFT) AND OF A GREEN TURTLE (_Chelone midas_) (TO THE RIGHT).
×⁵⁄₈. (Brit. Mus.) (After Reynolds.)
The cartilaginous portions are dotted.
1. basilingual plate or body of the hyoid.
2. hyoid arch.
3. first branchial arch (anterior cornu).
4. second branchial arch (posterior cornu).]
_III. The Ribs and Sternum._
_The Cervical Ribs._ As noted above, all of the cervical vertebræ
possess ribs. The first rib, attached to the atlas, consists of a
single, long blade projecting backward at an acute angle (Fig. 17, 8)
as far as the middle of the fourth vertebra. As described above it
articulates with the atlas at but one place. All of the other cervical
ribs have two articular surfaces, a tuberculum and a capitulum, with a
well-marked vertebrarterial canal between them. The ventral surface or
capitulum articulates with a short process on the centrum; the dorsal
surface or tuberculum (7) articulates with the transverse process. The
third to seventh ribs are somewhat T-shaped, the stem of the T being
the tubercle and head, while the cross arm of the T extends parallel to
the axis of the neck (Fig. 17, 7). In the eighth rib the posterior arm
of the T is elongated and projects out at a wide angle from the body;
and in the ninth or last cervical rib this arm extends laterally as far
as the vertebral portion of the thoracic ribs and has a cartilaginous
tip.
_The Thoracic Ribs_ (Figs. 16 and 26). These are ten in number, the
first eight pairs being connected with the sternum. The fourth may be
taken as typical. It consists of a bony vertebral portion and partially
ossified intermediate and sternal portions. The vertebral portion
articulates with its corresponding transverse process by two surfaces,
as described in connection with the thoracic vertebræ. In the first
and second ribs only the tuberculum articulates with the transverse
process, the head having a separate articular surface on the side of
the centrum, as in the typical cervical rib. In the last thoracic rib
the head and tubercle are not distinguishable from each other. Near
the distal end of all the vertebral portions except the first and the
last two ribs is a caudally projecting, partially ossified, uncinate
process. The intermediate portion is present in all but the tenth rib,
and wherever present, except in the ninth rib, it articulates distally
with the sternal portion. The sternal portions extend medio-cephalad in
a direction at right angles to the intermediate portion; the first two
articulate with the sternum, the next six with the xiphisternal horns,
and the ninth and tenth are missing.
[Illustration: FIG. 26. STERNUM AND ASSOCIATED MEMBRANE BONES OF A
CROCODILE (_C. palustris_). ×¹⁄₃. (Brit. Mus.) (After Reynolds.)
The last pair of abdominal ribs which are united with the epipubes by
a plate of cartilage have been omitted.
1. interclavicle.
2. sternum.
3. sternal rib.
4. abdominal splint rib.
5. xiphisternal horn.]
_The Abdominal Ribs_ (Fig. 26, 4). While these ribs are membrane
bones and are not homologous with the other ribs, they may as well be
mentioned at this time. They consist of about seven V-shaped sets of
slender bones, the point of each V being directed cephalad. Each V is
made up of from two or five slender bones, the number and arrangement
being subject to considerable variation. The last V of the series
(not well shown in the figure) is considerably larger than the rest
and is made up of four curved bones that extend around the anterior
ends of the pubic bones and are united to them by a broad tough
membrane. The first or most anterior V is united by a narrow membrane
(not shown in the figure) with the membrane that extends between the
xiphisternal horns. All of the V’s are more or less connected with each
other by fibrous membranes. Since these ribs lie superficial to the
recti muscles of the ventral body wall they are sometimes missing in
carelessly prepared skeletons.
_The Sternum_ (Fig. 26). The sternum consists of the cartilaginous
sternum proper (2), the xiphisternal horns (5), and the bony episternum
or interclavicle (1). The latter is an elongated, flattened bone of
somewhat spatulate outline, lying in the midventral line; it projects
forwards to about the sixth cervical vertebra, while the anterior edge
of the sternum is below the eighth cervical. Lying dorsal and lateral
to the episternum is the flat, almost membranous sternum, to the
posterior border of which the first two thoracic ribs are attached.
The xiphisternum consists of two long, slender rods of cartilage; the
anterior ends of these rods are in contact with each other and with the
posterior border of the sternum; from this point they gradually diverge
from each other as they extend caudad. A membrane extends between the
horns as far back as the attachment of the last thoracic ribs.
_IV. The Appendicular Skeleton._
_The Pectoral Girdle_ and _Anterior Limb_. The pectoral girdle (Fig.
27) is of a very simple type, consisting, unless the episternum
(interclavicle) be counted, of but two bones, the _scapula_ (_s_) and
_coracoid_ (_c_). The former consists of an upper, flat, paddle-shaped
portion and a thicker lower portion which articulates anteriorly with
the coracoid, and posteriorly forms about half of the notch-like
glenoid cavity. The dorsal edge of the flattened portion is continued
as a small, cartilaginous suprascapula. The coracoid is a flattened
bone, wide at either end and narrow in the middle, so that in a dorsal
view it is shaped like an hourglass. It is decidedly curved, with the
convex side down. Its outer edge articulates with the scapula and is
thickened to form the anterior border of the glenoid cavity. Its median
end is attached to the sternum. Near its scapular articulation there
is a well-marked foramen that passes entirely through the bone. The
_episternum_ (_e_) or interclavicle was described in connection with
the sternum and ribs. There is no clavicle nor other coracoid elements.
[Illustration: FIG. 27. PECTORAL GIRDLE AND ANTERIOR LIMB.
_c_, coracoid; _ce_, centrale; _cl_, claw; _e_, episternum; _h_,
humerus; _m_, metacarpals; _p_, pisiform; _r_, radius; _r′_, radiale;
_s_, scapula; _u_, ulna; _u′_, ulnare.]
The _anterior limb_ consists of the usual parts,--the upper arm,
forearm, and manus. The _humerus_ (Fig. 27, _h_) is rather thick in
proportion to its length; it has an elongated articular surface at
its proximal end for articulation with the glenoid cavity, and a
larger, somewhat bilobed surface for articulation with the radius
and ulna. On its ventral side, near the proximal end, is a very
prominent protuberance, the deltoid ridge. The _ulna_ (_u_) is slightly
heavier and longer than the radius and forms the greater part of the
elbow joint and about half of the wrist joint. Its proximal end is
considerably larger than the distal, but has no olecranon process. Its
distal end articulates with the ulnare and pisiform. The ulna as a
whole is slightly curved, while the radius is quite straight.
The _radius_ (_r_) consists of a cylindrical shaft with enlargements
of about equal size at the ends. The proximal end articulates with the
side of the ulna and with the humerus; the distal end with the radiale.
The carpus consists of a proximal row of three distinct bones and
a distal row of smaller and less fully ossified elements. Of the
proximal row the _radiale_ (_r′_) is much the largest bone. It is
hourglass shaped, with the proximal end somewhat larger than the
distal. Proximally it articulates mainly with the radius but also
slightly with the ulna and ulnare. Distally it articulates with the
centrale. The _ulnare_ (_u′_), the second bone in size in the wrist,
has about the same shape as the radiale but is much smaller. Proximally
it articulates with the pisiform, radiale, and, apparently, with the
ulna; distally it is in contact with the fused carpalia elements. The
_pisiform_ (_p_) is a small, irregular bone, articulating with the
ulna and the ulnare; it is apparently connected by a long ligament with
the fifth metacarpal but does not actually articulate with it. The
_centrale_ (_ce_) is a flattened, partially ossified element between
the radiale and the first and second metacarpals. The distal carpal
bones are represented by two irregular, partially ossified elements
between the ulnare and the third, fourth, and fifth metacarpals.
The manus proper consists of five digits. The _metacarpals_ (_m_)
are of about the same shape, but vary in length and thickness; each
consists of a cylindrical shaft with a slight enlargement at each end.
The first digit or pollex has two phalanges, the second has three,
the third has four, the fourth has four, and the fifth has three. The
terminal phalanx of each of the first four digits is pointed, has a
pair of lateral grooves, and is encased in a large, horny _claw_ (_cl_).
_The Pelvic Girdle_ and _Posterior Limb_. The pelvic girdle is
described differently by Wiedersheim and Reynolds; the bone called by
the former the pubis, the latter calls the epipubis. The bone called by
Wiedersheim the pubis takes no part in the formation of the acetabulum;
the pubis of Reynolds helps form the acetabulum but is a very small,
unossified structure. Gadow also calls the lower bone the epipubis. I
shall follow Reynolds’s interpretation.
The _ilium_ (Fig. 28, 1) is a heavy bone with a dorso-laterally
projecting crest; medially it is firmly united to the sacral ribs (Fig.
18, 5) while its outer side forms the upper and greater part of the
acetabulum. Its outer and lower border has two surfaces, the larger
and more posterior articulating with the ischium, the other with the
cartilaginous pubis.
[Illustration: FIG. 28. PELVIS AND SACRUM OF AN ALLIGATOR (_Caiman
latirostris_). ×¹⁄₂. (Brit. Mus.) (After Reynolds.)
1. ilium.
2. ischium.
3. true pubis.
4. epipubis (so-called pubis).
5. acetabular foramen.
6. neural spines of sacral vertebrae.
7. symphysis ischii.
8. process bearing prezygapophysis.]
The _ischium_ (2) is a slightly arched bone, its ventral end a
flattened blade articulating with its fellow, its dorsal end enlarged
and thickened to articulate with the ilium, pubis, and epipubis. This
dorsal end, which forms the ventral side of the acetabulum, is divided
into two distinct articular surfaces by a deep, rounded notch; the
posterior and larger surface articulates with the ilium, the anterior
surface about equally with the pubis and epipubis.
The _pubis_ (3), which is much the smallest element of the pelvis, is a
small mass of cartilage lying between the ilium above and the ischium
below. It forms a small part of the anterior wall of the acetabulum.
The _epipubis_ (4) is a slightly arched bone, somewhat enlarged at its
proximal end where it unites with the ischium, and flattened out into
a fan-shaped extremity, where it is united with its fellow and with
the last pair of abdominal ribs by the broad, thin sheet of cartilage
or fibrous tissue noted in connection with the abdominal ribs. As
mentioned above, it is called by Wiedersheim and others the pubis. Near
the center of the acetabulum there is a small foramen.
The _posterior limb_ (Fig. 29) consists of the usual divisions--thigh,
shin, and foot. The _femur_ (f) is a bone of the same general outline
as the humerus, though slightly longer and heavier. The head, for
articulation with the acetabulum, is rather hemi-elliptical than
hemispherical in shape, the long axis of the ellipse being vertical.
The distal enlargement is of at least as great, if not greater, bulk
than the proximal and shows some indication of a division into two
articular surfaces. The ventral side of the femur near the proximal end
shows a fairly distinct trochantal ridge.
The shin or crus is made up of two well-developed bones, the
_tibia_ (t) and _fibula_ (fb), the former being somewhat longer and
considerably thicker than the latter.
[Illustration: FIG. 29. POSTERIOR LIMB.
_ca_, calcaneum or fibulare; _cl_, claw; _f_, femur; _fb_, fibula;
_t_, tibia; _t³_, _t⁴⁻⁵_, tarsalia; _tb_, _tb′_, tibiale-centrale;
_IV_, _V_, 4th and 5th metatarsals.]
The tibia consists of a cylindrical shaft with enlargements of about
equal size at the ends. The proximal end forms most of the knee joint,
the distal end articulates with a tarsal element said by Reynolds to
represent the fused astragalus and centrale, by Wiedersheim called the
astragalus, and said to represent the united tibiale, intermedium, and
centrale (tb, tb′). The fibula articulates by a small enlargement at
its proximal end with the femur, and by an enlargement of about equal
size, at its distal end, with the fibulare or calcaneum (ca), and with
a small facet on the above-mentioned tibiale-centrale element.
The tarsus is much modified and consists of four elements, in two rows;
those of the proximal row are much larger than the two distal elements.
Articulating with both tibia and fibula, as mentioned above, and with
the first metatarsal and one of the distal tarsalia, is the large and
irregular _tibiale-centrale_ element of Reynolds (tb, tb′). In the
tarsus here shown it consists of two elements. Post-axial in position
is the _calcaneum_ or _fibulare_ (ca), articulating with the preceding
tarsal element, with the fibula, with the rudimentary fifth metatarsal,
and with the distal tarsal element said by Reynolds to represent the
fourth and fifth tarsalia. The calcaneum is extended caudad into a
prominent knob quite like the heel of the higher mammals.
The two distal tarsal bones are small; one is said by Reynolds to
represent the first three _tarsalia_ (t³), the other (t⁴⁻⁵) the fourth
and fifth. Wiedersheim says one of these bones represents the first
three tarsalia, the other the fourth. In the tarsus here shown these
two elements are fused.
The foot has five digits, though the fifth is small and consists merely
of a small, distally pointed metatarsal bone. According to Wiedersheim
this fifth metatarsal is fused with the fifth tarsalia. The metatarsals
of the first four digits are long and progressively more slender from
the first to the fourth; each is distinctly enlarged at the ends. The
first digit or hallux has two phalanges, the second has three, the
third has four, and the fourth has four. According to Reynolds, the
fourth toe has five phalanges; the figure here shown, which was drawn
from nature, has only four on the fourth toe; the latter is the number
given by Bronn for the crocodiles. The terminal phalanges of the first
three digits are large and pointed, with the same lateral grooves noted
in connection with the fore foot; each is sheathed in a horny claw. The
four fully developed digits of the pes are nearly twice as long as the
corresponding digits of the manus, but they are not proportionately
thicker.
CHAPTER III
THE MUSCLES
The description of the muscles here given is taken from Bronn (11),
who, in turn, largely follows Gadow. The animal described is the
crocodile, but while Bronn does not indicate the species, it is
probable that the differences between the various members of the
Crocodilia would be slight. The figures of the muscular system are
mainly from the Florida alligator.
In his description Bronn gives for each muscle the various synonyms
(often more than half a dozen) that are employed by different writers;
in this work Bronn’s nomenclature is given first and the synonyms
follow in parentheses.
THE CHEWING MUSCLES
_Temporalo-maxillaris_ (Temporalis) (Masseter, Temporal, Aeussere ober
Heber or Schlafmuskel). Arises in the temporal fossa, passes under the
zygoma, and inserts itself on the inner and outer sides of the lower
jaw.
_Pterygo-maxillaris_ (Pterygoideus) (Pterygoidien, Aeusser
Flügelmuskel, Pterygoideus externus, Pterygoideus internus). A large
muscle which consists of two portions: the outer, weaker portion
springs from the pterygoid process, the inner stronger part from the
pterygoid fossa and pterygoid process; they run together around the
angle of the lower jaw, where they form a large, bulging fold. They
are the chief muscles of this part of the body since the masseter is
lacking and the temporalis is weakly developed.
_Occipito-maxillaris_ (Digastricus maxillæ) (Niederzieher des
Unterkiefers, Abaisseur ou l’analogue du digastrique, Senker des
Unterkiefers, Aristotelis apertor oris, Digastricus, Aperator oris).
Arises from the hinder border of the lateral occipital and is inserted
at the hinder end of the lower jaw. Its course is from front to back.
If the skull be stationary this muscle drops the lower jaw; if the jaw
be fixed it raises the skull.
MUSCLES OF THE VENTRAL SURFACE OF THE NECK
_Intermaxillaris_ and _Sphincter Colli_ (Intermaxillaire,
Mylo-hyoideus, Zwischenkiefermuskel, Latissimus colli). This muscle
consists chiefly of transversely running fibers, and has in its
middle third a small, median, longitudinal raphe or aponeurosis. In
the posterior part of the neck it is very thin, but increases in
thickness more and more as it passes cephalad. A short anterior and a
long posterior portion may be distinguished. The former extends from
the inner side of the right to that of the left half of the lower jaw,
without a median aponeurosis. The hinder half of this muscle is united
by a pair of aponeuroses to the lower jaw, on one hand (the smaller
part), and to a fascia, on the other hand (the far larger part),
that separates several of the neck muscles. The smaller part begins
immediately behind the pterygoid on the inner side of the halves of the
lower jaw but ends on the outer side of the two halves of the jaw.
_Latus Colli_ (Latissimus colli accessorius). Lies underneath the
preceding. Its muscle bundles lie between the collo-capitis muscle and
the bodies of the first three cervical vertebræ, and form a broad band
that extends from the hyoid bone to the backwardly directed cervical
ribs of the first and second pairs.
_Coraco-ceratoideus_ (Omo-hyoideus, Coraco-hyoideus). A long, narrow,
and moderately thick muscle which takes its origin from the upper
border of the coracoid, where the latter touches the scapula. It
extends forward near the œsophagus and attaches itself to about the
middle of the backwardly turned border of the horn of the hyoid of that
side.
_Episterno-ceratoideus_ (Niederzieher des Zungenbeins, or
Brustbeinzungenbeinmuskel, Sterno-hyoideus). A flat and fairly broad
muscle which springs from the ventral surface of the episternum;
behind, it is separated by a slight space from the corresponding muscle
of the other side, with which it nearly covers the cervical part of the
trachea. Towards its anterior end it divides into two heads; one of
these inserts itself on the outer border and outer surface of the cornu
of the hyoid; the other head, lying laterad to the former, is suddenly
reduced to a short tendon by which it is attached to the following
muscle.
_Maxillo-coracoideus_ (Mylo-hyoideus anterior, Sterno-maxillare). This
muscle arises from the upper border and inner surface of the caudal
third of the lower jaw. In its further course it becomes tendinous
and projects by a short tendon outwards from the hyoid cornu to unite
with the head of the preceding muscle, as noted above; it then becomes
fleshy again and is inserted on the medial part of the upper border of
the coracoid.
_Maxillo-hyoideus_ (Genio-ceratoidien, Hyomaxillaris, Hyoglossus,
Hyomandibularis, Mylo-hyoideus posterior). This muscle arises, very
thin, from the mandibular symphysis, goes thence immediately backward
and inward to insert itself, by its broad end, on the whole anterior
end of the horn of the hyoid and on the hyoid itself.
_Cerato-hyoideus._ Arises from the horn of the hyoid and inserts itself
on the body of the hyoid.
_Costo-coracoideus._ This muscle arises from the distal ends of the
first and second ribs and is inserted on the ventral surface of the
coracoid at the boundary of the scapula.
_Costo-scapularis_ (Collo-scapularis superficialis, Levator scapulæ
superficialis). See shoulder muscles.
_Costo-vertebralis Medialis_ (Scaleni). Fairly large, flat, and
long-drawn-out three-cornered muscle. Attached by its base to the most
anterior sternal rib, by its upper border to the fifth cervical rib,
and by its point to the end of the second cervical rib.
_Costo-vertebralis Lateralis_ (Longus colli). Originates thin and sharp
on the body of the fifth thoracic vertebra, increases in thickness
slowly but decidedly cephalad, then again becomes thinner and inserts
itself on the inner side of the ribs of the most anterior two cervical
vertebræ.
_Collo-capitis_ (Rectus capitis anterior). Arises, as a rule, from the
cervical centra, at times from the second thoracic vertebra (Gavialis).
It extends forward and is inserted on the basi-occipital and the hinder
border of the pterygoid. For a greater part of their length the two
muscles lie close together, but forward they separate somewhat from
each other.
DORSAL NECK MUSCLES
_Occipito-cervicalis Medialis_ (Complexus cervicis, Biventer cervicis,
Zweibäuchiger Strecker or Zweibäuchiger Nackenmuskel, Splenius
capitis). It springs, by separate points, from the dorsal processes of
the four anterior body vertebræ and the six posterior neck vertebræ;
it is convex on its dorsal, weakly concave on its ventral surface; it
leads cephalad as a short, strong tendon by which it is attached to
the angle between the upper hinder border of the skull, _i.e._ to the
superior and lateral occipital region.
_Squamoso-cervicalis Medialis_ (Kopfbäuchmuskel [Splenius] or
durchflochtener Muskel [Complexus], Trachelo-mastoideus, Complexus).
This muscle lies laterad and ventrad to the preceding and is at times
partly covered by it in its posterior half. It arises from separate
heads from the spinal processes of the two anterior and six posterior
cervical vertebræ; beginning caudad, thin and sharp, it gradually
becomes thicker as it passes cephalad until it becomes partially
tendinous and inserts itself on the hinder border of the squamosal,
laterad to the occipito-cervicalis medialis muscle.
_Epistropheo-vertebralis_ (Splenius colli). This muscle springs from
the spinous processes of the most anterior three body vertebræ and the
last cervical vertebra; it receives fibers from the articular processes
and intermediate parts of the six posterior cervical vertebræ and is
inserted on the second cervical vertebra.
_Collo-squamosus_ (Splenius capitis, Nackenwarzenmuskel,
Trachelo-mastoideus). Springs from the upper transverse processes of
the last three neck vertebræ, and, becoming tendinous, is inserted on
the hinder border of the squamosal.
_Collo-occipitis._ Arises from the transverse processes of the
posterior five cervical vertebræ, extends directly forwards on the ribs
of the vertebræ, and is inserted under the articular surface of the
lateral occipital.
_Occipito-epistropheus_ (short, straight, hinder head-muscle, or
extensor). This muscle springs from the lateral surface of the body of
the second neck vertebra and inserts itself on the basi-exoccipital,
under the preceding muscle.
_Cervicalis Adscendens._ Arises in great part from the angles under
the most anterior ribs; a smaller part appears farther above where it
is covered by the rhomboideus muscle. It is inserted on the upper side
of the five posterior cervical ribs and on the distal ends of the long
second cervical rib.
THE MUSCLES OF THE SCAPULA
_Capiti-sternalis_ (Sterno-mastoideus). This is a fairly large muscle,
on the side of the neck, that extends from the skull to the breast
and from the middle of the neck is divided into two portions: (a) an
anterior part or atlanti-mastoideus (Plate I., Figs. 1 and 2, cst¹)
(upper end of the “head nodder,” sterno-mastoideus, anterior part
of sterno-mastoideus, anterior part of atlanti-mastoideus); (b) a
posterior part or sterno-atlanticus (Plate I., Figs. 1 and 2, cst²)
(sterno-mastoideus, inner belly of the “head-nodder,” posterior part of
the sterno-atlanticus). The former part is a rather short but not weak
muscle that arises from the squamosum and inserts itself on the rib of
the atlas (alligator) or of the atlas and epistropheus (crocodile).
The latter part is fairly strong and exceeds the anterior part in
length; it springs from the rib of the first cervical vertebra,
opposite the insertion of the anterior part, and inserts itself on the
anterior border of the outer surface near the episternum. At times
superficial fibers pass into the pectoral fascia.
_Dorso-scapularis_ (Cucullaris) (Plate I., Figs. 1 and 2, Cu)
(Trapezius). A broad but thin muscle that begins as an aponeurosis from
the dorsal fascia in the middle line of the hinder part of the neck
and beginning of the back; with converging fibers it passes within
to insert itself partly on the spine of the scapula and partly by
superficial fibers in the fascia that cover the deltoides scapularis
inferior muscle.
_Collo-scapularis Superficialis_ (Plate I., Fig. 1, cssp) (Levator
scapulæ superficialis, Levator scapulæ, Heber des Schulterblatts,
Acromio-trachélien, Teil des Serratus magnus, Levator anguli scapulæ).
A considerable muscle on the side of the neck. It arises from the tips
of the ribs of the first and second cervical vertebræ (where it is
fused with the sterno-atlanticus muscle), and also from the transverse
process of the third and fourth cervical vertebræ; it goes with
diverging fibers to the entire anterior border of the scapula.
_Thoraci-scapularis Superficialis_ (Serratus superficialis, Pectoralis
minor, Hinterer Theil des inneren grösseren Rückwärtsziehers, Pars
posterior m. serrati antici majoris, Theil des Grand dentelé, Serrati
posteriores, Latissimus dorsi scapulo-costalis). A strong muscle of
three prongs that go directly, by superficial fibers, over into the
oblique abdominal muscle and meet the ribs. The first and smallest
prong arises from the under end of the rib of the ninth vertebra (last
cervical); the second and medium-sized prong comes from the uncinate
process of the tenth rib (first thoracic) and from beneath the uncinate
process of the second thoracic rib; the third and strongest prong takes
its origin from the uncinate processes of the second and third thoracic
ribs. All three prongs unite to form a broad, homogeneous muscle which
passes forward and above to the hinder border of the scapula, upon
whose entire surface, except at the lower end, it is inserted.
_Collo-thoraci-suprascapularis Profundus_ (Plate I., Fig. 3, cthspr)
(Levator scapulæ et serratus profundus, Serrati anteriores, Serratus
anticus major, Vorderer Theil des inneren grösseren Rückwärtsziehers
or vorderen grossen gezahnten Muskels, Pars anterior m. serrati antici
majoris, Theil des Grand dentelé, Theil des Serratus magnus). This
muscle arises in varying extent from the transverse process of the
fifth cervical vertebra to the first (crocodile) or second (alligator)
ribs. It is inserted on the inner surface of the suprascapula, except
on its forward part, and is made up of two layers--a superficial and a
deep one. The former layer (Fig. 3, cthspr¹) is weakly developed and
is composed of two or three thin, distinct bundles, that extend from
the ribs of the eighth, ninth, and eleventh vertebræ (alligator) or
from the transverse process of the seventh vertebra and the rib of the
tenth. The deeper layer is considerably developed; its bundles come, in
the alligator, from the fifth to tenth vertebræ; in the crocodile from
the fifth to ninth.
_Rhomboideus_ (Plate I., Fig. 3, rh) (Rautenmuskel, Angulaire de
l’omoplate). This is a very small, independent muscle that springs, by
two or three distinct bundles, from the fascia covering the longissimus
dorsi muscle, in the region of the eighth and ninth vertebræ; after
a short course it inserts itself on the antero-dorsal angle of the
suprascapula.
_Costo-coracoideus_ (Plate I., Fig. 3, cc) (Subclavius et Triangularis
sterni and Levator secundæ superioris costæ, Petit dentelé, Pectoralis
minor, Pectoralis). This is a broad muscle of considerable size on the
ventral side of the breast; it consists of a lateral and of a medial
portion, the former springing from the last cervical rib, the latter
from the anterior border of the first sternocostal ridge. The two parts
unite and are inserted on the whole posterior border of the coracoid.
_Pectoralis minor_ (Pectoralis, Costo-coracoideus). A broad,
considerable muscle on the under side of the breast, which is made up
of two parts, of which the lateral springs from the anterior border of
the last (ninth) cervical rib, and the medial from the anterior border
of the first sternocostal ridge. Both parts unite into a homogeneous
layer which is inserted broadly on the whole hinder border of the
coracoid.
_Pectoralis_ (Plate I., Figs. 1 and 2, p) (Pectoralis major, Grosser
Brustmuskel). A broad muscle on the under side of the breast, bounded
behind by the rectus abdominis and obliquus abdominis externus muscles,
with which it is united. It arises from the whole episternum, from
the whole sternum, except from the median line of its posterior part,
from the sternal ends of the first six thoracic ribs, from all six
sternocostal ridges, and, with a small prong, from the eighth rib. It
is inserted on the distal part of the convex surface of the processus
lateralis humeri.
_Supracoracoideus_ (Plate I., Figs. 1 and 2, spc)
(Supracoracoscapularis, Deltoideus, Schlüsselbeinhälfte, Theil der
Schulterblatthälfte des Hebers des Armes, Obergrätenmuskel, Hebemuskel
des Oberarmes, Epicoraco-humeralis). A muscle of considerable size
at the anterior region of the coracoid and the under region of the
scapula, which is divided into two parts: (a) the coracoid (inferior)
division is the stronger and arises from the whole anterior half of the
coracoid, from its outer and inner surfaces; it is inserted, together
with the second part, on the proximal, little-developed part of the
processus lateralis humeri; (b) the scapularis (superior) division
is the weaker of the two and is covered by the deltoides scapularis
inferior muscle; it arises from the surface of the under third of the
scapula, behind the spine; it unites with the preceding part to form a
single muscle and inserts itself, as said above, on the proximal part
of the processus lateralis humeri.
_Coraco-brachialis_ (Brevis) (Plate I., Figs. 4, 5, and 6, cbb)
(Theil des grossen Brustmuskels oder Hakenarmmuskel, Pectoralis II.,
Pectoralis minor). A fairly strong muscle. It arises from the outer
surface of the coracoid, except the median edge and the anterior
section, and runs to the flexor surface of the upper arm where it is
inserted on the proximal third between the lateral and median processes.
_Coraco-antebrachialis_ (Plate I., Figs. 2 and 5, b¹) (Biceps,
Coracoideus, Langer Kopf des langen Beugers, Langer Kopf des Biceps,
Biceps humeri, Biceps brachii, Coraco-radialis). A slender and
rather weak muscle on the flexor side of the upper arm. It arises by
a fairly broad but thin tendon from the outer surface of the coracoid
immediately before the coraco-brachialis. As a weak bundle it passes
between the lateral and median processes, lying medially near the
brachialis inferior muscle, with which, at the end of the upper arm, it
unites; after their union the two muscles continue as a broad tendon
that splits into two parts, which are inserted on the proximal end of
the radius and of the ulna.
_Humero-antebrachialis Inferior_ (Plate I., Figs. 2 and 6, hai)
(Brachialis inferior, Caput breve m. bicipitis, Kurzer Kopf des Biceps,
Brachial interne, Brachialis anticus, Erster vom Oberarm ausgehender
Beuger, Portion of Brachiæus). Springs from the lateral flexor side of
the humerus, from the distal end of the lateral process to the distal
end of the bone, except the epiphysis; at the end of the upper arm it
unites with the biceps and with it is inserted, by two tendons, to the
radius and ulna.
_Dorso-humeralis_ (Plate I., Fig. 1, dh) (Latissimus dorsi, Breiter
Rückenmuskel, Humero-dorsalis). It springs as an aponeurosis from
the back at the level of the first four or five dorsal vertebræ, and
passes, with converging fibers, cephalo-ventrad to unite with the teres
major muscle; in common with the latter it extends along the extensor
surface of the humerus to be inserted between the lateral and median
processes.
_Dorsalis Scapulæ_ (Plate I., Fig. 1, dss) (Deltoides scapularis
superior, Unterer Theil des äusseren Schulterblattmuskels,
Untergrätenmuskel, Suprascapularis, Infraspinatus, Supraspinatus).
Springs from the anterior half of the outer surface of the scapula,
passes between the deltoides scapularis inferior and the caput
scapulare laterale externum m. anconæi, as a narrow band, to be
inserted on the lateral side of the humerus.
_Deltoides scapularis Inferior_ (Plate I., Figs. 1 and 2, dsi)
(Deltoideus superior, Supra- and Infraspinatus, Theil der
Schulterhälfte des Hebers des Armes, Theil der oberen [Schulterblatt-]
Abtheilung des Deltoideus, Zweiter Hebemuskel des Oberarmes, Theil des
Deltoides). A strong muscle on the side of the shoulder. It springs
from the spine of the scapula, passes back with slightly converging
fibers, and ends chiefly on the outer surface of the processus
lateralis humeri, while a number of superficial fibers end in the
humero-radialis muscle.
_Scapulo-humeralis Profundus_ (Plate I., Fig. 4, shpr) (Teres minor,
Erster Teres major, Scapulo-humeralis). A small muscle that springs
from the posterior border of the lower third of the scapula, and
passes, with converging fibers, to its insertion on the humerus just
distal to the medial process.
_Teres Major_ (Grosser runder Muskel oder kleiner Rückwärtszieher des
Oberarmbein, Zweiter teres major). Springs from the posterior half of
the upper region of the outer surface of the scapula. It passes down,
with converging fibers, to unite with the latissimus dorsi muscle to
form a strong tendon that is inserted on the extensor surface of the
humerus.
_Subscapularis_ (Unterschulterblattmuskel). Springs from the inner
surface of the scapula, except from the suprascapula, goes with
converging fibers directly over the capsule of the shoulder joint to be
attached to the medial process of the humerus.
_Anconæus._ This strong muscle lies on the extensor side of the upper
arm. It is made up of two layers: the superficial comes from the
pectoral girdle in two heads: (a) the caput scapulare laterale externum
and (b) caput coraco-scapulare; the deeper layer originates on the
humerus by three heads, (c) caput humerale laterale, (d) caput humerale
posticum, and (e) caput humerale mediale. These five heads of the
anconæus muscle with their synonyms will now be described.
(a) _Caput Scapulare Laterale Externum_ (Plate I., Figs. 1 and 4,
asl) (Brevi proximum caput m. tricipitis, Gewöhnlicher [äusserer]
langer Kopf des dreiköpfigen Streckers, Portion scapulaire externe
du triceps-brachial, Erster langer Kopf des Triceps, [Zweiter]
abducirender vom Schultergerüst entstehender Kopf des Streckmuskels
des Vorderarmes, Triceps Nr. 1, Triceps longus). This muscle springs
as a tendon from the hinder border of the scapula directly beneath
the articular cavity, and extends back, between the scapulo-humeralis
profundus and the dorsalis scapulæ muscles, into the muscle belly.
(b) _Caput coraco-scapulare_ (Plate I., Figs. 2, 4, 5, 6, acs)
(Externum caput m. tricipitis, Innerer langer Kopf des dreiköpfigen
Streckers, Portion scapulaire interne du triceps-brachial, Zweiter
langer Kopf des Triceps, [Erster] abducirender vom Schultergerüst
entstehender Kopf des Streckmuskels des Vorderarmes, Triceps Nr. 2,
Triceps longus secundus). Arises by two distinct tendinous tips--the
upper, weaker one from the hinder border of the scapula, the lower,
broader one from the hinder border of the coracoid.
(c) _Caput Humeri Laterale_ (Plate I., Figs. 1 and 4, ahl) (Brevius
caput m. brachiei interni, [Aeusserer] kurzer Kopf des dreiköpfigen
Streckers, Portion huméral externe du triceps brachial, Aeusserer vom
Humerus ausgehender Kopf des Streckmuskels des Vorderarmes, Theil des
Triceps Nr. 3, Triceps externum). Springs from the lateral part of the
extensor surface of the humerus dorsal to the lateral process and the
origins of the humero-radialis and brachialis superior.
(d) _Caput Humerale Posticum_ (Plate I., Fig. 4, ahp) (Longissimum
caput m. brachiei internum, Theil des inneren [kurzen] Kopfes des
dreiköpfigen Streckers, Theil des Triceps Nr. 3, Theil des Triceps
internus, Theil der Portion humérale interne du triceps brachial,
[Mittler] vom Humerus ausgehender Kopf des Streckmuskels des
Vorderarmes). Springs from the middle of the extensor surface of the
humerus between the lateral and medial heads.
(e) _Caput Humerale Mediale_ (Longius caput m. brachiei interni, Theil
des [inneren] kurzen Kopfes des dreiköpfigen Streckers, Theil der
Portion humérale interne du triceps brachial, [Innerer] vom Humerus
ausgehender Kopf des Streckmuskels des Vorderarmes, Theil des Triceps
Nr. 3, Theil des Triceps internus). This head originates on the medial
part of the extensor surface of the upper arm at the end of the medial
process where it is united with the scapulo-humeralis profundus muscle.
The muscle mass formed by the union of all the above heads goes over,
as a broad and somewhat thick tendon, to become inserted on the
proximal part of the ulna.
_Humero-radialis_ (Plate I., Figs. 1 and 4, hr) (Caput longum m.
bicipitis, Eigener kurzer Beuger, [Zweiter] vom Oberarm ausgehender
Beuger, Brachialis externus, Portion _a_ of Brachiæus). A fairly large
muscle on the outer side of the upper arm, lying between the brachialis
inferior and caput humerale laterale muscles, with both of which it
is, at the beginning, united. It originates with its deeper and chief
mass from the outer surface of the humerus, just distal to the lateral
process; while its superficial layer, especially the upper fibers, come
directly from the deltoides scapularis inferior and therefore have
their origin on the scapula. In the middle of the upper arm it becomes
a slender round tendon that extends, through a tendinous loop, to the
radius, on whose outer side, at the end of the proximal third, it is
inserted.
MUSCLES OF THE FOREARM
_Humero-radialis Internus_ (Radialis internus, Lange Vorwärtswender,
Pronateur, Pronator teres, Pronator quadratus, Oberflächlich gelegener,
langer runder Einwärtsdreher). This muscle arises from the condylus
internus (C. ulnaris s. medialis) and attaches itself to the radius
throughout almost its entire length. It is a fairly strong muscle.
_Ulno-radialis_ (Carré pronateur, Pronator teres, Pronator quadratus,
Muskel welcher dem Pronator quadratus entsprecht). A strongly developed
muscle. It springs from the upper part of the flexor surface of the
ulna and is inserted on the lower part of the flexor surface of the
radius.
_Humero-radialis Longus_ (Plate II., Figs. 1 and 2, _1_) (Supinator
longus, Long supinateur, Lange Rückwärtswender, Supinator radii
longus). Among the Crocodilia this and the following muscle are well
developed. This one springs from the condylus externus humeri and is
inserted on the outer side of the entire length of the radius.
_Humero-radialis Brevis_ (Plate II., Fig. 4, _d_) (Supinator brevis,
Kurze Rückwärtswender, Extensor carpi-radialis brevis [?]). Arises near
the preceding from the external condyle of the humerus and is inserted
at the upper end of the radius.
_Humero-carpi-radialis_ (Plate II., Fig. 2, _a_) (Aeusserer oder langer
Speichenmuskel, Musculus quem parti superiori extensoris digitorum
communis respondere videbat, Extensor carpi-radialis longus, Abductor
pollicis longus). Towards the ulna, near the supinator longus muscle.
It springs from the external condyle of the humerus, covers the
supinator brevis muscle, and is inserted on the proximal end of the
carpi-radialis.
_Humero-carpi-ulnaris_ (Plate II., Fig. 2, _c_) (Extensor
carpi-ulnaris, Ulnaris externus). Originates on the external condyle of
the humerus, is inserted on the proximal end of the os carpi-ulnare.
_Humero-metacarpalis III., IV., V._ (Plate II., Fig. 2, _b_) (Extensor
digitorum longus, Aeusserer Speichenmuskel or Speichenstrecker der
Hand, Extenseur commun, Extensor radialis longus, Extensor digitorum
communis). This muscle lies between the humero-carpi-radialis and the
humero-carpi-ulnaris muscles. It springs from the condylus externus
humeri and divides, on reaching the carpus, into three thin, flat
tendons, which in part fuse with the carpo-phalangei muscle, and in
part are inserted on the carpal bones of the third, fourth, and fifth
fingers.
_Carpo-phalangei_ (Plate II., Fig. 2, _d_). (Extensor digitorum brevis,
Extenseurs courts, Gemeinschaftlicher Strecker der Hand, Extensor
digitorum communis brevis). Springs from the carpal and, in part, from
the metacarpal bones and is inserted on the terminal phalanges of the
five fingers.
_Ulno-carpi-radialis_ (Ein dem Strecker und Abzieher des Daumens
analoger Muskel, Extensor pollicis longus, Extensor carpi-radialis
brevior[?]). Springs from the under half of the ulna, and is inserted
on the os carpi-radiale.
_Carpo-phalangeus I._ (Extensor pollicis brevis). This is a small,
thick muscle that originates on the distal part of the os carpi-radiale
and is inserted on the phalanx of the thumb.
_Humero-radialis Lateralis_ (Plate II., Fig. 1, _6_) (Flexor
carpi-ulnaris, Innerer Ellenbogenmuskel, Ulnaris internus). A fairly
strongly developed muscle. It springs from the internal condyle of the
humerus, extends along the ulna, and is inserted on the proximal part
of the os carpi-ulnare, and the nearby pisiform bone.
_Humero-radialis Medialis_ (Plate II., Fig. 1, _2_) (Flexor
carpi-radialis, Radialis internus). A strongly developed muscle. It
springs from the internal condyle of the humerus, receives fibers from
almost the entire length of the radius, and is inserted on the proximal
end of the os carpi-radiale and with a thin tendon to the metacarpal
bone of the thumb. Rüdinger was not able to find this muscle in
_Alligator cynocephalus_.
_Carpo-phalangei_ (Plate II., Fig. 1, _4_) (Flexor digitorum communis
brevis, Oberflächlicher gemeinschaftlicher Fingerbeuger, Fléchisseur
sublime, Flexores sublimis a profundo perforati, Lange Flexoren der
Finger, Flexor digitorum communis sublimis s. brevis, Flexor digitorum
sublimis). A small thick muscle. It springs from the ligamentum
carpi-volare proprium and from the ulnar border of the distal end of
the os carpi-radiale and is divided into eight muscle-bellies which
pass over to the proximal ends of the first phalanges as thin tendons
that are penetrated by those of the humero-ulno-phalangei muscle.
_Humero-ulno-phalangei_ (Plate II., Figs. 1 and 2, _5_) (Flexor
digitorum communis profundus, Fléchisseur profond, Tiefer
gemeinschaftlicher Fingerbeuger, Flexor digitorum profundus, Flexor
profundus). Arises with three heads. The first head takes its
origin from the internal condyle of the humerus, runs between the
humero-radialis lateralis muscles, and passes as a tendon over to the
carpus where it unites with the other two heads of this muscle. The
second, deep head comes from almost the entire length of the ulna.
These two heads may be called the long heads. The third, short head
springs from the proximal ends of the two large carpal bones of the
first row, and becomes united radially with the thick flat tendon
ending the first two heads. The common terminal tendon splits into four
points which pass among the tendons of the carpo-phalangei muscle and
are inserted on the terminal phalanges. From the terminal tendons of
this muscle spring the lumbricales muscles.
_Carpo-phalangeus_ (Plate II., Fig. 1, _8_) (Abductor pollicis).
Springs from the os carpi-radiale; is inserted on the first phalanx of
the thumb.
_Carpo-metacarpalis I._ (Plate II., Fig. 1, _9_) (Opponens pollicis).
Originates from the os carpi-radiale and is inserted on the radial side
of the entire first metacarpus.
_Metacarpo-phalangeus I._ Originates from the base of the metacarpus of
digit III.; is inserted on the ulnar side of the first phalanx of the
thumb.
_Pisiformi-phalangeus primus digiti V._ (Plate II., Fig. 1, _7_)
(Abductor digiti minimi, Abducteur du petit doigt, Abductor digiti
quinti). Springs from the pisiform bone, and is inserted on the medial
border of the first phalanx of the fifth finger.
_Carpo-metacarpalis V._ (Opponens digiti minimi, Opponens primus).
Springs from the carpi-ulnare bone and is inserted on the metacarpal
bone of the fifth digit.
_Carpo-phalangeus primus digiti V._ (Plate II., Fig. 1, _3_) (Flexor
digiti minimi brevis, Opponens secundus). Arises from the ulnar border
of the proximal part of the carpi-radiale bone and is inserted on the
proximal end of the first phalanx of the fifth finger.
_Metacarpo-phalangeus I. digiti V._ (Adductor digiti minimi). Springs
from the metacarpal bones of the second and third fingers and is
inserted on the radial side of the first phalanx of the fifth finger.
THE ABDOMINAL MUSCLES
_Obliquus Abdominis Externus_ (Grand oblique, Aeusserer schiefer
Bauchmuskel, Obliquus externus, Obliquus externus + internus +
Serrati, Oblique descendens). Springs, with a flat prong, from the
uncinate processes of the true ribs, thence it extends as a tendinous
aponeurosis, near the lateral boundary of the ileo-costalis muscle,
caudal-ward to the region of the twenty-third (crocodile) vertebra.
From this fairly straight line of origin the muscle takes a sharply
distoventral course and is inserted, at least in part, on the outer
surface of the sternal part of the ribs of the tenth to sixteenth
vertebræ, but does not reach the mid-ventral line. Under this chief
part of the outer layer of the abdominal muscle lies a second, more
band-like muscle mass which is also strong but of considerably less
extent. It takes its origin from the outer surface of the middle third
of the ribs. In the region of the twentieth vertebra it fuses with the
upper layer, but inwardly reaches nearer the median line than the upper
layer.
_Obliquus Abdominis Internus_ (Petit oblique, Obliquus internus,
Subcostalis). Arises as a flat muscle layer first with a strong
tendinous portion from the anterior dorsal border of the os pubis and
from the there-located cartilaginous inscriptio tendinea of the rectus;
second, by a dorsal portion, with a short tendon, from the anteromedial
surface of the pubo-iliac articulation from the pubis and ilium
equally; third, from the dorsal anterior ends of the last named bones.
It is inserted somewhat mediad to the lateral border of the rectus
ventralis muscle that covers it on the outside.
_Transversus Abdominis_ (Transverse, Oblique Bauchmuskel, Innerer
Bauchmuskel, Transversus ventralis). This muscle springs by short,
flat, indistinct forks from the inner surface of the proximal ends of
the dorsal ribs but does not reach the centra of the vertebræ because
of the long, broad transverse processes. Caudally the origin passes
dorsalward to the lateral border of the quadratus lumborum muscle
between which and the ileo-costalis muscle it is attached to the end of
the transverse process.
_Rectus Abdominis_ (Gerader Bauchmuskel + pyramidenförmiger Muskel,
Pyramidalis, Rectus abdominis + pyramidalis). This muscle consists, in
the Crocodilia, of several very distinct parts:
I. The rectus ventralis, the chief part, arises as a fleshy tendon from
the sternum and from the ventral part of the last rib that reaches
the sternum, and extends with direct longitudinal fiber-bundles of
equal mass over the ventral third of the body back to the pelvis. It
is inserted as a fleshy tendon on the anterior border of the pubis and
more laterally is united, together with the obliquus internus muscle,
chiefly to the last abdominal ribs which arise as an ossification of
the last strongly developed inscriptio tendinea. This muscle-band,
which unites with that of the opposite side to form the linea alba, is
divided metamerically by seven distinct inscriptiones tendinea. These
inscriptiones are the above described abdominal ribs which consist
of bony connective-tissue without a trace of cartilage cells. These
so-called abdominal ribs, then, are not true ribs but are ossifications
of the tendinous structures.
II. From the anterior border of the os pubis and the last strong
inscription, also, to some extent, as a process of the preceding
part, begins a new fleshy layer which, extending in diminishing size
backward, is inserted by a strong tendon on the distoventral end of the
ischium somewhat laterad to the symphysis. It is the muscle that is
called by different authors the pyramidalis.
III. Rectus lateralis. About in the region of the twentieth vertebra,
or at the level of the fifth inscription, a fleshy band-like muscle
separates itself from the edge of the rectus muscle and the obliquus
internus muscle and passes over to fuse with the ischio-coccygeus
muscle.
IV. Rectus internus. On the inner surface of the rectus ventralis, from
which it is separated by the intervening aponeurosis of the rectus
muscle, appears a muscle lying on the outside of the diaphragmatic
muscle. It extends as a broad band from the breast to the anterior
border of the os pubis, with longitudinally directed fibers, to half
the width of the rectus ventralis muscle.
_Intercostales_ (Zwischenrippenmuskeln). The intercostal muscles in
the Crocodilia are, in proportion to the strength of the ribs, of
slight structure; they extend only from rib to rib and are, therefore,
very short, though fairly thick. They, as usual, consist of the outer
muscles with a direction like that of the external oblique, and of an
inner muscle extending in the opposite direction, _i.e._, at right
angles. The internal muscles are especially well developed in the
breast region and pass over into the internal oblique muscle.
_Quadratus Lumborum_ (Carré des lombes, Viereckiger Lendenmuskel, Psoas
major). A strong, thick muscle that springs from the inner surface
of the transverse processes and bodies of the last six presacral and
the first sacral vertebræ. The muscle diminishes as it passes in a
caudoventral direction and is inserted with a strong tendinous band to
the trochanter femoris.
_The Diaphragm_ (Diaphragmaticus, Zwerchfell, Bauchfellmuskel).
Closely inclosed between the skin and muscle of the abdomen, in the
Crocodilia, is a pair of muscles; they are, as a whole, thin muscles
that are widely separated and extend in an anteroposterior direction.
Each arises by two parts which, however, are united at the pelvis.
One of these parts is small at its beginning, is fairly thick, and is
attached by a short tendon, immediately over the pubis in front of the
hip joint, to the ilium. The other part is not a very thick layer,
and is attached, by a fairly long line, partly on the inner surface
of the hindermost abdominal rib and partly on the outer border of the
pubis. After the union of these two portions the muscle extends farther
forwards and the fibers of the stronger portion spread out like a fan,
becoming wider and thinner as they go forward and are at last attached
partly to the pericardium, partly to the lobes of the liver of that
side of the body. To be more exact, the fibers of the diaphragmaticus
that lie nearest the middle line of the belly-wall extend forward as a
fairly broad band to fuse with the pericardium. Most of the fibers of
this muscle, however, are in close connection with a fibrous membrane
which surrounds the liver parenchyma; this membrane is mostly very
thin but it gradually becomes thicker towards the hinder border of
the liver. Other muscle bands do not reach so far as the liver but
are located near the middle line of the back; they are all, however,
attached to an aponeurosis which passes over the upper, hinder border
of the liver lobes to fuse with the fibrous capsule of the liver.
To the sternum as to the ribs is only a small part of this muscle
attached.
Between the two above described muscles is found a space which is
filled, in great part, with a fibrous membrane that binds the two
muscles together. This membrane begins very thin and without a marked
boundary behind the kidneys; it runs forward directly under them and
the dorsal wall of the body, becoming gradually thicker, though never
very thick, and fuses, laterad to the kidneys, with the above-mentioned
aponeurosis of the two diaphragmaticus muscles. Thence this aponeurosis
goes to the upper, hinder side of the liver where it becomes fairly
thick. One thus finds in front of the stomach a fibrous membrane,
belonging to the diaphragmaticus, which is pierced by the œsophagus and
by a fairly large space that extends around the œsophagus and between
it and the liver. This membrane fastens the liver to the œsophagus.
The muscle of the right side is covered, on almost its entire inner
surface (from its hinder end to the liver) by the belly-like skin, and
is fairly closely united with it. The left muscle, on the other hand,
is only covered by this skin from the hinder border of the stomach
forwards; farther forward it lies immediately on the under and left
side of the stomach and is united with it by loose connective-tissue.
Outwardly both muscles are united by a thin layer of connective-tissue
to the true abdominal muscles. So far as yet known this muscle is not
present in other reptiles.
MUSCLES OF THE POSTERIOR APPENDAGES
_Ambiens_ (Plate III., Figs. 1 and 2, amb, Plate IV., Figs. 2 and
4, amb, Plate V., Figs. 2 and 3, amb) (Part I., Rectus femoris and
Sartorius partim, Vastus internus, Innere Streckmuskelmasse) (Part II.,
Gracilis, Rectus femoris, Sartorius). Arises by a short tendon from the
anterior spine of the ilium, near its union with the pubis. The muscle
swells quickly to a thick belly which, lying under the skin on the
forward and inner side of the upper thigh, is again reduced to a small,
flat tendon which extends abruptly over the anteromedial surface of the
knee joint to its outer side; it then passes through the complex of
tendons of the femoro-tibialis muscle, beneath which it unites with the
tendon of origin for the peroneus posterior muscle.
To this muscle is the following strange muscle to be ascribed (Part
II): it springs, small in extent, from the inner surface of the os
pubis near the acetabulum, extends thence forward around the pubis, and
runs into a long, thin tendon which unites with the insertion tendon of
the subcutaneous extensor ilio-tibialis muscle.
_Extensor Ilio-tibialis_ (Plate III., Fig. 2, ex. il. tb.) (Part I.,
Rectus femoris, Adductor flexor, Glutæus maximus; M. du facia lata,
Vastus externus, Tensor faciæ latæ, Tensor femoris vaginæ, Glutæus
minimus, Tensor faciæ femoris). This muscle, in the Crocodilia,
consists of two parts:
I. The chief part is long and broad, and springs as a tendon from more
than the anterior half of the lateral border of the dorsal crest of the
ilium, covering the origin of the ilio-fibularis muscle. Its insertion,
by a broad, flat tendon, overlying the femoro-tibialis muscle, together
with the tendon of this muscle, is on the anterior surface of the head
of the tibia.
II. The second, significantly smaller and narrower, part arises outside
of the quadratus lumborum by a short tendon from the most dorsal end of
the ilium; it goes over, medially, along the nearer head of the ambiens
muscle, then to the anteromedial side of the upper leg, into the
deeper-lying femoro-tibialis muscle.
_Femoro-tibialis_ (Plate III., Fig. 1, fm. tb., Plate IV., Fig. 2, fm.
tb., Plate V., Figs. 1 and 3, fm. tb.) (Cruræus et Vasti, Cruralis).
Arises by an anterior inner and a posterior outer head; both heads
arise from the outer-anterior and inner surfaces of the femur, and
unite with each other and with the extensor ilio-tibialis and ambiens
muscles as a strong tendon, which extends over the knee and is inserted
on the anterior border of the head of the tibia; this tendon incloses,
like a sheath, the end-tendon of the ambiens muscle.
_Ilio-fibularis_ (Plate III., Fig. 2, il. fib., Plate IV., Fig. 2,
il. fib., Plate V., Fig. 3, il. fib.) (Biceps cruris, Semitendinosus +
Semimembranosus, Glutæus maximus, Abductor fibularis, Flexor abductor
cruris). This consists, in the Crocodilia, of two entirely separate
small, band-like muscles. The first springs by a short tendon from
the lateral surface of the middle ilium, very near the origin of the
caudali-ilio-femoralis and extensor ilio-tibialis muscles. The chief
part of the end-tendon is inserted at the end of the first sixth of the
fibula, on its outer-forward corner near the origin of the peroneus
anterior muscle; a shorter tendon-branch goes to the tendon of the
peroneus posterior muscle; and a third, still smaller branch goes to
the caput femorale of the gastrocnemius muscle, by which it contributes
to the structure of the lateral part of the tendo-communis externus.
The second part springs, by an equally short tendon, very near the
first, from the hinder end of the dorsal crest of the ilium, goes
directly over the preceding to the knee, where its tendon unites with
that of the extensor ilio-tibialis muscle.
_Ilio-femoralis_ (Plate III., Fig. 2, il. fm., Plate IV., Fig. 2, il.
fm., Plate V., Fig. 1, il. f.) (Glutæus, Quadratus femoris [?], Glutæus
medius). This muscle is inwardly fused with the caudali-ilio-femoralis,
whose anterior part it forms.
_Caudali-ilio-femoralis_ (Plate III., Fig. 2, cd. il. fm., Plate
IV., Fig. 1, cd. il. fm.) (Zweiter Auswärtsroller, Extensor femoris
caudalis accessorius, Glutæus minimus). This forms a thick mass that
springs directly from the lateral surface of the anterior and middle
parts of the ilium, is covered outside by the ilio-fibularis muscle,
and, pushing between the two heads of the femoro-tibialis muscle, is
inserted on the whole outer surface of the middle third of the femur.
_Caudi-femoralis_ (Plate III., Figs. 1 and 2, cd. fm., Plate
IV., Fig. 1, cd. fm.) (Pyriformis, Pyriformis + Subcaudalis,
Femoro-peroneo-coccygeus, Extensor femoris caudalis). This muscle in
the Crocodilia consists of two parts:
I. The chief part extends from the first postsacral (the twelfth)
vertebra caudad; it springs from the roots of the caudal ribs
(transverse processes) and the whole lateral surface of the vertebral
arches. Since the first postsacral vertebra has no ventral process, the
muscles of the opposite sides fuse in the mid-line. Towards the caudal
region it gradually increases in strength. Its fibers converge in a
lateroventral direction to form a short, thick tendon which attaches
itself to the inner surface of the femur mediad and somewhat below the
trochanter. At right angles from this tendon extends a round, long
tendon which, lying parallel to the hinder side of the thigh, pushes
in between the chief parts of the ischiadicus and later between the
origin-tendon of the gastrocnemius and peroneus posterior muscles, and
is inserted on the posterior surface of the head of the fibula.
II. This is a more anterior and inner muscle, small in size, which
has a fleshy origin from the bodies and ribs (transverse processes)
of the second sacral and first caudal vertebræ at a distance from the
posteromedian border of the ischium. It extends caudad, lying near the
hinder part of the pubi-ischio-femoralis externus, and is inserted on
the trochanter.
_Flexor Tibialis Externus_ (Plate III., Figs. 1, 2, 3, fl. tb. ext.
or f. t. ext., Plate IV., Fig. 4, fl. tb. ext., Plate V., Figs. 1
and 3, fl. tb. ext. and f. t. ext.) (Triceps flexor cruris partim,
Biceps). A strong, spindle-shaped muscle that arises, together with the
ilio-fibularis, by a short tendon, from the side of the portio dorsalis
of the ilium, and in the neighborhood of the bend of the knee is split
into two tendons, of which the short one is inserted on the fibular
side of the neck of the tibia, while the other, running along near the
caput femoris of the gastrocnemius muscle, unites with the tendon of
the caput tibiæ of the gastrocnemius muscle just beyond the ankle joint.
_Flexor Tibialis Internus_ (Plate III., Figs. 1, 2, 3, fl. tb. int., or
f. t. int., Plate IV., Fig. 4, fl. tb. int., Plate V., Fig. 1, fl. tb.
int.) (Demi-nerveux + Demi-membraneux, Triceps flexor cruris partim,
Gracilis, Adductor flexor tibialis, Semimembranosus, Semitendinosus
+ Gracilis partim, Gracilis + Semimembranosus + Semitendinosus). A
three-headed muscle whose heads arise separately and first unite in
the region of the lower leg as a short, strong tendon. Their origins
are as follows: (1) As a band from the anterior margin of the ischium,
pushing between the ischio-femoralis and the pubi-ischio-femoralis
externus muscles; (2) From the posterior margin of the ischium as
a narrow, tendinous band near the insertion of the ischio-caudalis
muscle; (3) from the portio-dorsalis posterior of the ilium,
ventralward, near the origin of the flexor tibialis externus muscle.
_Ischio-femoralis_ (Plate III., Fig. 1, is. f.) (Adductores, Adductor
longus, Adductor primus). Springs directly (without tendon) from the
entire anterior border of the ischium. It is band-like and, running
over the tendon of the pubo-femoralis internus and externus muscle, is
inserted as a broad, fleshy tendon on the middle third of the inner,
posterior surface of the femur.
_Pubi-ischio-femoralis Externus_ (Plate III., Fig. 1, p. is. f. int.,
Plate IV., Fig. 1, p. is. f. int.) (as a whole: Quatuor pectinei
[partim]; in parts: I. Marsupialis externus, Obturator externus; II.
Quadratus femoris). This muscle arises in two parts. The anterior part
is broad and comes from the entire ventral and inwardly turned outer
surface of the pubis. Its insertion is on the femur in conjunction
with the first part of the pubi-ischio-femoralis internus. The
second part is shorter but thicker than the first and springs from
almost all of the outer surface of the ischium that is not covered
by the origins of the ischio-femoralis, pubi-ischio-tibialis, and
flexor tibialis internus muscles. It is inserted, by a strong, short
tendon, on the trochanter, somewhat caudad to the insertion of the
pubi-ischio-femoralis internus.
_Pubi-ischio-femoralis Internus_ (Plate III., Fig. 1, p. is. f. int.,
Plate IV., Figs. 1 and 2, p. is. f. int.) (as a whole: Iliacus internus
+ Quatuor pectinei [partim]; in parts: I. and II.: Kamm-Muskeln,
Pectineus inferior [I.] + superior [II.], Marsupialis internus,
Obturator internus; III., Iliacus [Darmbeinmuskel], Iliacus internus).
This muscle arises by two or three parts: I. The anterior arises,
without tendon, from the greater part of the inner and anteriorly
directed surface of the pubis; median to this, in the alligator, is
a small bundle, II., which unites with part I. These unite with the
pubi-ischio-femoralis externus to form a strong tendon that is inserted
on the trochanter.
III. This is a larger muscle that springs without tendon from the inner
surface of the body and transverse processes of the twenty-fifth and
twenty-sixth (in alligator) vertebræ, from the part of the ilium that
lies between these transverse processes and the ischium, and from a
small part of the ischium. It is inserted on the whole inner surface of
the proximal third of the femur.
_Pubi-ischio-femoralis Posterior_ (Plate III., Fig. 1, p. is. f. post.,
Plate IV., Figs. 1 and 4, p. is. f. post. and pb. is. f. m. post.)
(Adductus [partim], Gemellus, Obturator internus). Springs without
tendon from the whole caudally directed border of the ischium. It is
inserted, by a short tendon, near and laterad to the tendon of the
ischio-femoralis muscle, on the hinder surface of the upper leg.
_Extensor Longus Digitorum_ (Plate V., Figs. 2 and 3, ext. l. [long.]
dig.) (Long extenseur commun, Gemeinschaftlicher Fussheber oder Beuger,
Extensor communis digitorum). Springs, together with the tibialis
anticus, from the external condyle of the femur, goes with this muscle
under the ligamentum tibio-fibulare and after union with this divides
into four short tendons. Three of these tendons are inserted on the
fibular side of the bases of the first three metatarsal bones; the
fourth goes over into the muscle of the third toe.
_Tibialis Anticus_ (Plate III., Fig. 1, tib. ant., Plate IV., Fig. 4,
tib. ant., Plate V., Figs. 2 and 3, tib. ant.) (Jambier antérieur,
Vorderer Schienbeinmuskel). Springs by a fleshy tendon from the
anterior surface of the head and neck of the tibia and quickly unites
with the following muscle.
_Peroneus Anterior_ (Plate V., Figs. 2 and 3, peron. ant.) (Peroneus
longus). In the alligator. Its origin: it extends from the insertion
of the ilio-fibularis muscle distalwards by the whole outer surface of
the fibula, under the skin and over the ligamentum tibio-fibulare, and
gives off a broad, tendinous portion to help strengthen the tendon
Achilles, which portion may be followed to the rudiment of the fifth
toe. On the outer side of this toe rudiment is attached a tendon from
the tibial border of the muscle.
In the crocodile. This muscle is here divided into two parts, of
which the one that springs from the anterior surface of the fibula
is inserted on the toe rudiment, while the greater and outward part
extends over the calcaneum bone and has the same distribution as in the
alligator.
_Peroneus Posterior_ (Plate IV., Figs. 3 and 4, peron. post., Plate
V., Figs. 2 and 3, peron. post.) (Plantaris). Springs chiefly from the
tendon of the ambiens muscle running over the knee and forms the direct
continuation of this muscle. Besides this come tendinous fibers from
the insertion tendons of the femoro-tibialis and extensor ilio-tibialis
muscles; and finally supporting fibers from the outer, end-tendon of
the ilio-fibularis muscle. The fibers of this muscle pass partly into
the fibular portion of the caput femoralis of the gastrocnemius, while
the chief mass of the muscle is inserted on the posterior surface of
the calcaneum.
_Gastrocnemius_ (Plate III., Figs. 1 and 3, cap. int. gastr., Plate
IV., Fig. 4, cap. int. gastr. and cap. ext. gastr., Plate V., Figs. 2
and 3, cap. ext. gastr. and cap. int. gastr.) (Solenmuskel, Outer head
of gastrocnemius). This is the strongest superficial flexor muscle on
the posterior surface of the lower leg; it consists of two heads: I.
The caput femorale (externum) originates by a strong, short tendon from
the lateral and posterior surface of the external condyle of the femur.
This head has a double insertion: (1) from the outer, fibular border of
the muscle separates off a tendon that spreads out in the first layer
of the plantar tendon-muscle; (2) the chief part of caput I. becomes
a broad, flat, subcutaneous tendon which is covered by the tendon
Achilles and serves as the origin of the short flexors of the toes.
II. The caput tibiale (internum) springs without a tendon from the
posterior surface of the head and the proximal third of the tibia. The
broad and somewhat flat muscle has two insertions: (1) on the plantar
and medial border of the first basis metatarsi; (2) the chief insertion
on the outer border of the rudimentary fifth toe, after forming, with
the tendon of the flexor tibialis externus, the tendon Achilles.
_Flexor Longus Digitorum_ (Plate IV., Fig. 4) (Langer durchbohrender
gemeinschaftlicher Zehenbeuger). A many-headed muscle visible on
the posterior side of the lower leg after removal of the preceding
muscle. (a) Caput externum: a flat, fairly broad muscle which springs
from the outer and posterior surface of the fibula. Arriving at the
astragalo-scaphoid bone, it forms a very strong tendon which unites
with the still stronger tendon of the other head and both together
form the broad initial tendon of the flexor digitorum communis brevis
muscle. (b) Caput internum: this springs without a tendon from the
whole posterior surface of the upper half of the tibia, sometimes, as
in crocodiles, uniting with the caput femoralis of the gastrocnemius
muscle. The common tendon splits into three points for the first,
second, and third toes.
_Tibialis Posticus_ (Plate V., Fig. 2, tib. post.) (Jambier postérieur,
Hinterer Schienbeinmuskel). Originates without tendon from the whole
fibular side of the tibia, on the one hand, and from the whole inner
and forward side of the fibula on the other hand, occupying the
whole space between these two bones on the hinder side of the lower
leg. At its proximal end it is united with the caput internum of the
preceding muscle which completely covers it from behind. It narrows
down to a very strong tendon which divides into two equally strong,
round tendons; of these the one on the tibial side is inserted on the
basis ossis of the first metacarpal, the one towards the fibula goes
immediately to the second metacarpal.
_Interosseus Cruris_ (Kniekehlmuskel). A small muscle stretching
between the distal ends of the fibula and tibia with almost transverse
fibers; it is covered dorsally by the tibio-fibulare ligament and
appears as a distal division of the tibialis posticus muscle.
_Flexor Digitorum Brevis_ (Flexor longus accessorius, Flexor brevis
perforatus). Springs from the bones of the foot and from the strong
tendon of the flexor digitorum longus muscle. It divides into three
bellies for the second, third and fourth toes. The first two are
pierced by the above-mentioned tendon of the flexor digitorum longus
and are inserted on the next to last phalanx of the second and third
toes; the third, on the contrary, is inserted on the claw joint of the
fourth toe and is not perforated; there is no tendon to the fourth toe
from the flexor digitorum longus muscle.
_Extensor Hallucis Proprius_ (Plate V., Fig. 3) (Kurzer
gemeinschaftlicher Zehenstrecker, Extensor hallucis). This muscle
springs by a short, flat, fairly strong tendon from the outer dorsal
border of the distal half of the fibula. It is inserted: (1) on the
proximal half of the first metatarsal bone, (2) a second much weaker
part is united with the tendon of insertion of the tibialis anticus
extensor longus digitorum to the first metatarsal bone.
THE TAIL MUSCLES
The muscles of the tail have, as shown by Gadow, the character of
the primitive body muscles, with their primitive metameric division,
fairly plainly preserved. This musculature is arranged in four rows
of trumpet-shaped cones, one projecting into the other, by which
arrangement each metamere exhibits a transverse zigzag line of four
anteriorly and three posteriorly directed points.
_Ilio-ischio-caudalis_ (Plate III., Figs. 1 and 2, is. cd., Plate
IV., Figs. 1 and 2, is. cd.) (Ischio-coccygeus). The crocodile is the
nearest to the typical condition in the musculature of the tail. The
lateral and ventral part of the tail musculature forms a broad mass
that extends to the end of the tail; it lies immediately under the skin
and springs from the caudal ribs (transverse processes--Gadow) and
from the spinous processes of all the caudal vertebræ. The entire side
musculature of the tail ends cephalad in several portions; the most
ventral and medial of these bound the cloaca as an at least slightly
developed, morphological sphincter; the lateral portion is attached
to the posteroventral border of the ischium; while the dorsal portion
is inserted by two heads on the first caudal rib and on the posterior
spine of the ilium.
PLATE I.
SHOULDER MUSCLES OF CROCODILUS ACUTUS. (From Bronn after Fürbringer.)
FIG. 1. SHOULDER MUSCLES AFTER REMOVAL OF THE SPHINCTER COLLI MUSCLE
(_sphr_).
FIG. 2. SHOULDER MUSCLES AFTER REMOVAL OF THE SPHINCTER COLLI MUSCLE
(_sphc_).
FIG. 3. DEEP LAYER OF THE INNER SHOULDER MUSCLES AFTER REMOVAL OF
THE HUMERUS AND ITS MUSCULATURE AS WELL AS THE COLLO-SCAPULARIS
SUPERFICIALIS MUSCLES (_cssp_) AND THORACI-SCAPULARIS SUPERFICIALIS
MUSCLES (_thcsp_).
FIG. 4. SHOULDER MUSCLES AFTER REMOVAL OF THE PARS SCAPULARIS OF THE
SUPRA-CORACO-SCAPULARIS (_sps_) AND OF THE BICEPS MUSCLE (_b_).
FIG. 5. DIFFERENT VIEW OF FIG. 4.
FIG. 6. SHOULDER MUSCLES AFTER REMOVAL OF THE PARS CORACOIDEA OF THE
SUPRA-CORACO-SCAPULARIS (_spc_) AND DELTOIDES SCAPULARIS SUPERIOR
(_dss_) MUSCLES.
LETTERING FOR ALL FIGURES OF THIS PLATE.
_acs_, _ahl_, _ahp_, _asl_, coraco-scapular, humerale laterale,
humerale posticum, and scapulare laterale externum heads of
the anconæus muscle; _b_, coraco-antebrachialis (biceps); _c_,
coracoid; _cbb_, coraco-brachialis; _cc_, costo-coracoideus; _Cl_,
clavicle; _cssp_, collo-scapularis superficialis (levator scapulæ
superficialis); _cst_, capiti-sternalis (sterno-mastoideus);
_cthspr_, collo-thoraci-scapularis profundus (levator scapulæ and
serratus profundus); _cu_, dorso-scapularis (cucullaris); _dh_,
dorso-humeralis (latissimus dorsi); _dsi_, deltoides scapularis
inferior; _dss_, dorsalis scapulæ (deltoides scapularis superior);
_Ec_, epicoracoid; _Est_, episternum; _esthy_, episterno-hyoideus;
_H_, humerus; _hai_, humero-antebrachialis inferior (brachialis
inferior); _hr_, humero-radialis; _p_, pectoralis; _PL_, processus
lateralis humeri; _PM_, processus medialis humeri; _R_, radius;
_rh_, rhomboideus; _S_, scapula; _sbsc_, subscapularis; _shpr_,
scapulo-humeralis profundus; _spc_, supra-coraco-scapularis; _sphc_,
sphincter colli; _SpS_, spina scapulæ; _SS_, suprascapulare; _St_,
sternum; _Sta_, anterior part of sternum; _Stp_, posterior part
of sternum; _thssp_, thoraci-scapularis superficialis (serratus
superficialis); _U_, ulna; _V₅_, _V₆_, 5th and 6th vertebræ.
NERVES SHOWN IN THIS PLATE.
3_a_. thoracicus VII.
7. posterior branch of the thoracicus superior VII for the
collo-thoraci-suprascapularis profundus and rhomboideus
muscles.
7_a_. proximal.
7_b_. distal thoracicus superior VII.
10_a_. thoracicus inferior.
12. supra-coracoideus.
15. integumental, (13 and 14), muscular branch of the
supra-coracoideus.
19. pectoralis.
21. brachialis longus inferior.
29_b_. teres major.
31. dorsalis scapulæ (posterior).
32. cutaneus brachii and antebrachii superior lateralis.
32_a_. humero-radialis.
33. deltoides inferior, (25 and 42), cutaneus brachii and
antebrachii medialis.
[Illustration]
PLATE II.
FIGS. 1-4. MUSCLES OF THE FOREARM OF THE ALLIGATOR.
(From Bronn.)
FIGS. 5-7. (From Bronn after Rathke.)
FIG. 1. _1_, humero-radialis longus (supinator longus);
_2_, humero-radialis medialis (flexor carpi radialis); _3_,
carpo-phalangei I digiti V; _4_, carpo-phalangei (flexor digitorum
communis brevis); _5_, humero-ulno-phalangei (flexor digitorum
communis profundus); _6_, humero-radialis longus; _s._ flexor
carpi ulnaris; _7_, pisiforme-phalangeus primus digiti V; _8_,
carpo-phalangeus I; _9_, carpo-metacarpalis I.
FIG. 2. 1-5 as in FIG. 1; _a_, humero-carpi-radialis; _b_,
humero-metacarpalis III, IV, V (extensor digitorum longus); _c_,
humero-carpi-ulnaris; _d_, carpo-phalangei (extensor-digitorum
brevis).
FIG. 3. _a_, _b_, humero-ulno-phalangei (flexor digitorum communis
profundus).
FIG. 4. _a_, ulno-carpi-radialis; _b_, ulna; _c_,
humero-ulnaris-lateralis (flexor carpi ulnaris); _d_, humero-radialis
brevis (supinator brevis).
FIG. 5. HEAD, NECK, AND A PART OF THE BODY OF A CROCODILUS VULGARIS.
(Ventral View).
_a_, lower jaw; _b_, upper jaw; _c_, arch of palate; _d_, fold of
palate; _h_, pterygoideus internus (Rathke); _i_, pterygoideus
externus (Rathke); _k_, longus colli (Rathke); _m_, rectus capitis
anticus major (Rathke); _n_, sterno-mastoideus (Rathke); _o_, levator
scapulæ (Rathke); _p_, scalenus (Rathke).
FIG. 6. PART OF A SIMILAR PREPARATION OF C. RHOMBIFER.
_a_, the hindermost of the superior maxillary teeth; _b_, lower
jaw; _c_, wings of palate; _d_, pterygoid; _e_, quadrate; _g_,
intertransversalis (Rathke); _h_, trachelomastoideus (Rathke);
_i_, levator scapulæ (Rathke); _k_, longus colli (Rathke); _m_,
pterygoideus externus (Rathke); _n_, rectus capitis anticus major
(Rathke).
FIG. 7. A PART OF THE HEAD AND NECK OF ALLIGATOR LUCIUS.
_a_, pterygoideus externus (Rathke); _b_, digastricus (Rathke);
_c_, rectus capitis anticus major (Rathke); _d_, sterno-mastoideus,
anterior belly (Rathke); _e_, sterno-mastoideus, posterior belly
(Rathke); _f_, levator scapulæ (Rathke); _g_, cervicalis adscendens
(Rathke); _h_, longus colli (Rathke); _i_, intertransversalis
(Rathke); _k_, trachelomastoideus (Rathke); _l_, biventer cervicis
(Rathke); _m_, splenius colli (Rathke); _n_, splenius capitis
(Rathke).
[Illustration]
PLATE III.
FIG. 1. MUSCLES OF THE POSTERIOR EXTREMITY OF ALLIGATOR
MISSISSIPPIENSIS. LEFT SIDE, VENTRAL (PLANTAR) SURFACE.
FIG. 2. THE SAME, DORSAL AND LATERAL SURFACES.
FIG. 3. A. MISSISSIPPIENSIS; THE TENDONS OF THE FLEXOR TIBIALIS
MUSCLE IN THEIR RELATION TO THE GASTROCNEMIUS MUSCLE. RIGHT LEG,
INNER SURFACE. (FIGS. 1-3 from Bronn, after Gadow.)
_amb_, ambiens; _cap_, _ext_, _gastr_, external head of
gastrocnemius; _cap_, _int_, _gastr_, internal head of
gastrocnemius; _cd_, _fm_, caudali-femoralis; _cd_, _il_, _fem_,
caudi-ilio-femoralis; ex. il. tb. extensor ilio-tibialis; _ext_,
_l_ (_long_), _dig_, extensor longus digitorum; _fl_, _tb_, _ext_,
flexor tibialis externus; _fl_, _tb_, _int_, flexor tibialis
internus; _fm_, _tb_, femoro-tibialis; _il_, _cd_, ilio-caudalis;
_il_, _cost_, ilio-costalis; _il_, _fib_, ilio-fibularis; _il_, fm
(_il_, f), ilio-femoralis; _il_, _s_, _cd_, ilio-sacro-caudalis;
_is_, _cd_, ischio-caudalis; _is_, _f_, ischio-femoralis; _ob_,
_ext_, obliquus externus; _pb_, _cd_, pubi-caudalis; _pb_, _is_,
_tb_, pubi-ischio-tibialis; _pb_, _tb_, pubi-tibialis; _peron_,
_ant_, peroneus anterior; _peron_, _post_, peroneus posterior; _p_,
_is_, _f_, _ext_, pubi-ischio-femoralis externus; _p_, _is_, _f_,
_int_, pubi-ischio-femoralis internus; _p_, _is_, _f_, _post_,
pubi-ischio-femoralis posterior; _qudr_, _lb_, quadratus lumborum;
_rect_, rectus abdominis; _tib_, _ant_, tibialis anticus; _tib_,
_post_, tibialis posticus; _trans_, transversus abdominis; _tr_,
_per_, transversus perinei; _m_, _post_, _il_, posterior border of
ilium; _ob_, foramen in pubis for the obturator nerve; _o_, _il_,
ilium; _o_, _is_, ischium; _o_, _pb_, pubis; _o_, _cl_, cloacal bone;
_pr_, _l_, _pb_, lateral process of pubis; _pr_, _tr_, transverse
process; _sp_, _ant_, _il_, anterior spine of ilium; _Sy_, _p_,
symphysis pubis; _Sy_, _is_, symphysis of ischium; _tb_, _is_,
tubercle of ischium.
[Illustration]
PLATE IV. (From Bronn, after Gadow.)
FIG. 1. ALLIGATOR MISSISSIPPIENSIS. INNER SURFACE OF THE PELVIC
REGION, LEFT SIDE. THE PUBIS, ISCHIUM, AND VERTEBRÆ ARE CUT THROUGH
THE MEDIAN PLANE, XXVIII, 28th VERTEBRA.
FIG. 2. HATTERIA PUNCTATA.
FIG. 3. A. MISSISSIPPIENSIS. THE DEEPEST MUSCLES ON THE PLANTAR
SURFACE OF THE LEFT HIND FOOT. ROMAN NUMERALS IX-XII, SHORT TOE
MUSCLES.
FIG. 4. A. MISSISSIPPIENSIS. LEFT LEG FROM THE POSTERO-MESIAL
ASPECT. THE PLANTAR FLEXOR MUSCULATURE IN SITU, AFTER REMOVAL OF THE
GASTROCNEMIUS MUSCLE AND THE ASSOCIATED MUSCLES. ROMAN NUMERALS,
VI-X, SHORT TOE MUSCLES.
_amb_, ambiens; _cap_, _ext_, _gastr_, external head of
gastrocnemius; _cap_, _int_, _gastr_, internal head of
gastrocnemius; _cd_, _fm_, caudali-femoralis; _cd_, _il_, _fem_,
caudi-ilio-femoralis; _ex_, _il_, _tb_, extensor ilio-tibialis;
_ext_, _l_ (_long_), _dig_, extensor longus digitorum; _fl_, _tb_,
_ext_, flexor tibialis externus; _fl_, _tb_, _int_, flexor tibialis
internus; _fm_, _tb_, femoro-tibialis; _il_, _cd_, ilio-caudalis;
_il_, _cost_, ilio-costalis; _il_, _fib_, ilio-fibularis; _il_, _fm_
(_il_, _f_), ilio-femoralis; _il_, _s_, _cd_, ilio-sacro-caudalis;
_is_, _cd_, ischio-caudalis; _is_, _f_, ischio-femoralis; _ob_,
_ext_, obliquus externus; _pb_, _cd_, pubi-caudalis; _pb_, _is_,
_tb_, pubi-ischio-tibialis; _pb_, _tb_, pubi-tibialis; _peron_,
_ant_, peroneus anterior; _peron_, _post_, peroneus posterior; _p_,
_is_, _f_, _ext_, pubi-ischio-femoralis externus; _p_, _is_, _f_,
_int_, pubi-ischio-femoralis internus; _p_, _is_, _f_, _post_,
pubi-ischio-femoralis posterior; _qudr_, _lb_, quadratus lumborum;
_rect_, rectus abdominis; _tib_, _ant_, tibialis anticus; _tib_,
_post_, tibialis posticus; _trans_, transversus abdominis; _tr_,
_per_, transversus perinei; _m_, _post_, _il_, posterior border of
ilium; _ob_, foramen in pubis for the obturator nerve; _o_, _il_,
ilium; _o_, _is_, ischium; _o_, _pb_, pubis; _o_, _cl_, cloacal bone;
_pr_, _l_, _pb_, lateral process of pubis; _pr_, _tr_, transverse
process; _sp_, _ant_, _il_, anterior spine of ilium; _Sy_, _p_,
symphysis pubis; _Sy_, _is_, symphysis of ischium; _tb_, _is_,
tubercle of ischium.
[Illustration]
PLATE V. (From Bronn, after Gadow.)
FIG. 1. HATTERIA PUNCTATA. (Ventral View.)
FIG. 2. ALLIGATOR MISSISSIPPIENSIS. LEFT POSTERIOR EXTREMITY; FOOT
IN PRONATION, HENCE SEEN FROM THE DORSAL SIDE. _lg_, _t_, _f_,
LIGAMENTUM TIBIO-FIBULARE.
FIG. 3. A. MISSISSIPPIENSIS. MUSCLES OF THE DORSAL SURFACE OF THE
LOWER LEG AND FOOT.
_amb_, ambiens; _cap_, _ext_, _gastr_, external head of
gastrocnemius; _cap_, _int_, _gastr_, internal head of
gastrocnemius; _cd_, _fm_, caudali-femoralis; _cd_, _il_, _fem_,
caudi-ilio-femoralis; _ex_, _il_, _tb_, extensor ilio-tibialis;
_ext_, _l_ (_long_), _dig_, extensor longus digitorum; _fl_, _tb_,
_ext_, flexor tibialis externus; _fl_, _tb_, _int_, flexor tibialis
internus; _fm_, _tb_, femoro-tibialis; _il_, _cd_, ilio-caudalis;
_il_, _cost_, ilio-costalis; _il_, _fib_, ilio-fibularis; _il_, _fm_
(_il_, _f_), ilio-femoralis; _il_, _s_, _cd_, ilio-sacro-caudalis;
_is_, _cd_, ischio-caudalis; _is_, _f_, ischio-femoralis; _ob_,
_ext_, obliquus externus; _pb_, _cd_, pubi-caudalis; _pb_, _is_,
_tb_, pubi-ischio-tibialis; _pb_, _tb_, pubi-tibialis; _peron_,
_ant_, peroneus anterior; _peron_, _post_, peroneus posterior; _p_,
_is_, _f_, _ext_, pubi-ischio-femoralis externus; _p_, _is_, _f_,
_int_, pubi-ischio-femoralis internus; _p_, _is_, _f_, _post_,
pubi-ischio-femoralis posterior; _qudr_, _lb_, quadratus lumborum;
_rect_, rectus abdominis; _tib_, _ant_, tibialis anticus; _tib_,
_post_, tibialis posticus; _trans_, transversus abdominis; _tr_,
_per_, transversus perinei; _m_, _post_, _il_, posterior border of
ilium; _ob_, foramen in pubis for the obturator nerve; _o_, _il_,
ilium; _o_, _is_, ischium; _o_, _pb_, pubis; _o_, _cl_, cloacal bone;
_pr_, _l_, _pb_, lateral process of pubis; _pr_, _tr_, transverse
process; _sp_, _ant_, _il_, anterior spine of ilium; _Sy_, _p_,
symphysis pubis; _Sy_, _is_, symphysis of ischium; _tb_, _is_,
tubercle of ischium.
[Illustration]
CHAPTER IV
THE NERVOUS SYSTEM
SPINAL CORD
The spinal cord extends the whole length of the vertebral canal and
ends near the end of the tail as a thin, round thread. It varies in
thickness and shape in cross section, being nearly always elliptical,
but at places approaching a circle. Large, spindle-formed thickenings
of about equal diameter are present in the cervical and lumbar regions.
A cauda equina is absent in the alligator, the nerves of the large tail
leaving the cord like the intercostals.
On its ventral surface the cord has a deep perpendicular fissure, the
fissura ventralis, that extends almost to the center; it extends even
along the reduced region in the tail. A vascular membrane extends into
this fissure.
A shallow but distinct furrow extends along the dorsal side of the
cord, parallel to which, on either side, is a fine, linear furrow.
The first two spinal nerves have no dorsal roots.
BRAIN
The cervical cord passes insensibly into the medulla, the dorsal furrow
becoming wider and more shallow as it merges into the fourth ventricle.
A dorsal view of the brain is shown in Figure 30, A. The most prominent
structures here seen are the cerebral hemispheres, VH, whose combined
transverse diameter is greater than their longitudinal. The tapering,
cephalic end of each hemisphere forms an olfactory tract, I, which
extends cephalad to form the olfactory bulb, B. ol. Lying between the
caudal ends of the hemispheres is a small conical body, G.p., called by
Bronn and others the pineal body. The writer has found (62), however,
that this body is the paraphysis rather than the epiphysis. Caudad to
the cerebra-hemispheres and in contact with them are the optic lobes,
MH; they have about the same shape and position as in the frog, but are
much smaller in proportion to the size of the hemispheres. Immediately
caudad to the optic lobes is the cerebellum, HH, somewhat elliptical in
outline as seen from above.
Extending caudad from beneath the cerebellum is the medulla, NH, with
its triangular fourth ventricle. The outlines of the medulla are
somewhat obscured by the numerous roots of the eighth to eleventh
cranial nerves, VIII-XI, which arise along its dorsal border. The
medulla, as was said above, passes, as is usually the case, without
any line of demarcation into the spinal cord, the obex filling in the
apex of the fourth ventricle at the anterior end of the median dorsal
fissure.
[Illustration: FIG. 30. BRAIN OF ALLIGATOR. (A, dorsal; B, ventral; and
C, lateral view.) (From Wiedersheim, slightly altered.)
_VH_, cerebral hemispheres, each of which gives rise
postero-laterally to a hippocampal lobe partially overlying the
corresponding optic tract, _Tr.opt_; _ZH_, thalamencephalon; _MH_,
optic lobes; _HH_, cerebellum; _NH_, medulla oblongata; _I-XII_,
cranial nerves; _1_, _2_, first and second spinal nerves; _B.ol_,
olfactory bulb; _Tro_, olfactory tract; _G.p_, paraphysis; _Jnf_,
infundibulum; _Hyp_, hypophysis; _Med_, spinal cord.]
A lateral view of the brain is shown in Figure 30, C. The hemisphere,
VH, is conical in outline, with a small projection from the
posteroventral region; its continuation forwards as the olfactory
tract, Tro., and bulb, B. ol., is plain. Beneath it and extending
forwards are the prominent optic nerve, II, and tract. Caudad to the
latter and projecting ventrad and caudad are the infundibulum, Inf.,
and hypophysis, Hyp.
Caudad to the cerebrum are seen the end of the paraphysis, G.p., the
optic lobes, MH, and the cerebellum, HH. From the cerebral peduncles
(ventrad to the optic lobes) arises the oculomotor nerve, III, and
dorsocaudad to this, between the optic lobe and the cerebellum, arises
the trochlear nerve, IV. From the middle zone (in a dorsoventral
direction) of the medulla, ventrad to the cerebellum, arises the very
large trigeminal nerve, V; while from its usual place, on the ventral
surface of the medulla, the abducens nerve, VI, takes its origin by
several roots. At some distance caudad from the trigeminal, from the
dorsal surface of the medulla, as noted above, the very large acoustic
nerve, VIII, arises; and immediately ventrad to this, on the side of
the medulla, the facial nerve, VII, may be seen. Commencing just
caudad to the acoustic and extending along the upper border of the
medulla and beginning of the spinal cord, are seen a dozen or more
small nerve roots, which unite to form the glossopharyngeal, IX, vagus,
X, and spinal accessory, XI, nerves. Ventral to the roots of the
last, on the ventral surface of the medulla, arise the roots of the
hypoglossal nerve, XII. A short distance caudad to this nerve are seen
the first two spinal nerves, 1 and 2, which have, as noted above, no
dorsal roots.
A ventral view of the brain is shown in Figure 30, B. The cerebral
hemispheres, VH, have the same outline, of course, as in the dorsal
view, but the rounded projection from the caudal end of each is here
seen on each side of the infundibulum, Inf. The infundibulum is in
close contact with the chiasma anteriorly, and lies close between the
converging optic tracts, Tr. opt. From the chiasma the optic nerves,
II, extend, in an antero-lateral direction, almost at right angles to
each other. The appearance of the olfactory tracts, I, is the same
as in the dorsal view. Caudad to the infundibulum, from the cerebral
peduncles, ZH, arise the rather small oculomotor nerves, III. Caudad
to these, from near the ventral fissure, on the middle region of the
medulla, arise the abducens nerves, VI, and from the ventral side of
the posterior part of the medulla and of the anterior end of the cord
arise the hypoglossal, XII, and the first two spinal nerves, 1 and 2.
The origins of the other cranial nerves were described in connection
with the lateral view of the brain, where they show more clearly. On
each side of the cerebral peduncles is seen the ventrolateral edge of
the corresponding optic lobe. The pyramidal tracts are seen, extending
caudad from the region of the peduncles, as a swelling on each side of
the median ventral fissure.
THE CRANIAL NERVES (CROCODILE)
The origin of each of the cranial nerves was described in connection
with the lateral and ventral views of the brain. A full description
of the distribution of these nerves would require more space than the
limits of this book will allow, but a brief account will now be given.
I and II. The olfactory and optic nerves. These two large nerves go
immediately to their respective sense organs, so that no further
discussion of them need be here given.
III. The oculomotor nerve. The single stem divides into three branches:
a median, going to the externus rectus muscle; a lateral, going to
the inferior rectus muscle; and an intermedial, going to the inferior
oblique muscle.
IV. The trochlear (pathetic) nerve leads to the superior oblique muscle.
V. The trigeminal nerve. The distribution of this nerve is very
complicated. It has three main divisions: (1) the ophthalmic branch,
(2) the superior maxillary branch, and (3) the inferior maxillary
branch. (1) The ophthalmic in turn divides into two branches: the
smaller, frontal, going to the integument of the upper and lower
eyelids; the larger, nasal, going chiefly to the nasal cavity but also
sending some small branches to the upper and lower eyelids. (2) The
superior maxillary branch separates into a number of divisions: (a) a
branch that, in the neighborhood of the auditory capsule, fuses with
the facial nerve; (b) a twig to the integument of the forehead and to
the upper and lower eyelids; (c) a branch to the Harderian gland and
the conjunctiva; (d) a branch to the neighborhood of the cheek, to the
angle of the mouth, and to the palatine branch of the facial nerve; (e)
a branch to the palate; (f) a branch to the integument of the upper
jaw; (g) a branch to the teeth of the upper jaw. (3) The inferior
maxillary branch divides into four branches: (a) this division supplies
the skin of the cheek region; (b) a branch to the chewing muscles; (c)
a branch that divides into two nerves--the first going to the skin of
the lower jaw, the second dividing again into two nerves, both of which
lead to the integument of the lower jaw; (d) the fourth division of the
inferior maxillary, known as the inferior alveolar, itself divides into
two twigs--(a′) the first twig divides into two parts, a larger and a
smaller, both of which lead, by different paths, to the inner skin of
the mouth; (b′) the second twig divides into four parts--two leading to
the mylohyoid muscle and to the integument at the corner of the mouth,
one to the integumental glands at the corner of the mouth, and one to
the floor of the mouth cavity.
VI. The abducens nerve leads to the retractor oculi muscle and to the
muscle for the nictitating membrane.
VII. The facial nerve gives off three main branches: (1) the first
divides again into three twigs--(a) connecting with a branch of the
trigeminal nerve, (b) and (c) connecting with the trigeminal and also
leading to the palate; (2) the second branch divides into two twigs
that connect with the glossopharyngeal nerve; (3) the third branch
divides into two parts, a muscular twig, and the chorda tympani.
VIII. The auditory or acoustic nerve leads, of course, to the sensory
regions of the ear.
IX. The glossopharyngeal nerve divides into four main branches,
as follows: (1) to the larynx, (2) to the œsophagus, (3) to the
hyomaxillary and sterno-maxillary muscles, and (4) to the tongue. There
are also certain communicating twigs with the facial and vagus nerves.
X. The vagus or pneumogastric nerve gives off four branches: (1)
and (2) communicate with each other and supply the pharynx, larynx,
œsophagus, and trachea; (3) goes to the œsophagus; (4) goes to the
heart, lungs, and stomach.
XI. The spinal accessory nerve. There seems to be some doubt as to the
exact identity and distribution of this nerve, but Bronn says that,
according to Fischer, it gives twigs to the lower head-muscles and then
divides into fine branches in the atlanti-mastoideus muscle.
XII. The hypoglossal nerve, going to the region of the tongue,
divides into three branches: (1) the median and smallest goes to the
sterno-maxillary muscle; (2) the inner and larger goes to the same
muscle and also to the coraco-hyoid and sterno-hyoid muscles; (3) the
outer and largest divides into three twigs of which the first two
lead to the hyomaxillary and sterno-maxillary muscles respectively,
while the third divides into two twigs that lead to the hyoglossal and
genioglossal muscles respectively.
THE SPINAL NERVES
As was noted above, the dorsal roots of the first two spinal nerves are
lacking.
I, II, and III. The ventral branches of these three nerves supply the
smaller, ventral neck muscles.
IV. The ventral branch of this nerve innervates with its chief
divisions the ventral muscles, the sphincter colli, and the integument
of the neck, and sends a small branch to the levator scapulæ
superficialis muscle.
V. The ventral branch of this nerve sends branches to the ventral
muscles of the neck, to the levator scapulæ superficialis; a large
branch goes to the sterno-mastoid; and the rest of the nerve
distributes itself in the sphincter colli and the integument and
ventral muscles of the neck.
VI. The sixth nerve distributes itself to the ventral musculature and
to the integument of the neck, and sends a fairly strong branch to the
levator scapulæ superficialis muscle and to the most anterior part of
the collo-thoraci-suprascapularis profundus muscle.
VII. The seventh nerve is the first to enter, by a small branch, into
the brachial plexus (Figure 31). It also sends a branch to the ventral
muscles and the integument of the neck, and three branches to various
shoulder muscles.
VIII. The ventral branch of the eighth nerve (Figure 31) is the
second largest nerve of the brachial plexus. It gives some twigs
to the ventral muscles and then gives one or two nerves to the
collo-thoraci-suprascapularis profundus and the serratus superficialis
muscles. The rest of the nerve divides into an inferior and a superior
branch which unite with the ninth nerve.
IX. The ninth and tenth nerves are the largest of the brachial plexus.
The former, after giving off some twigs to the ventral musculature
and to the serratus superficialis and the hinder regions of the
collo-thoraci-suprascapularis profundus muscles, unites with the tenth
nerve just after giving off the small thoracicus inferior nerve to
the costo-coracoideus muscle. After uniting with the tenth nerve the
ninth nerve immediately divides into two branches that form loops with
branches of the eighth nerve, the whole making a very complicated
plexus.
X. The tenth nerve, as noted above, is one of the two largest nerves
of the brachial plexus. After giving off a single nerve to the ventral
musculature, this nerve unites with the eleventh nerve; it then gives a
branch to the costo-coracoideus muscle and forms a loop with the ninth
nerve. After giving off a couple of nerves it again divides into two
equal branches which unite with similar branches of the eighth nerve.
XI. The eleventh nerve is next to the smallest of the plexus.
Besides branches to the trunk musculature it gives a fine twig to
the integument of the axilla and unites with the tenth nerve in the
brachial plexus. This is the last nerve that enters into the brachial
plexus.
[Illustration: FIG. 31. BRACHIAL PLEXUS OF C. ACUTUS. (From Bronn,
after Fürbringer.)
VII-XI. ventral branches of seventh to eleventh spinal nerves.
3_a_. thoracicus anterior VII.
4. thoracicus superior V.
7. thoracicus superior VI.
7_a_. proximally-leading thoracicus superior.
7_b_. distally-leading thoracicus superior VIII.
9. thoracicus superior IX.
10_a_, 10_a₁_, 10_a₂_, 10_a₃_. thoracicus inferior.
18. cutaneus pectoralis.
19. pectoralis.
21. brachialis longus inferior.
22. coraco-brachialis.
22_c_. branch for the distal belly of biceps muscle.
24. muscular branch for the humero-antebrachialis inferior.
(25 + 42). cutaneus brachii and antebrachii medialis.
29. subscapularis.
31. dorsalis scapulæ (posterior).
32. cutaneus brachii superior lateralis.
33. deltoides inferior.
34. brachialis longus superior.
36. anconæus.
36_a_. scapulo-humeralis profundus.]
The distribution of the nerves of the brachial plexus is as follows
(Fig. 31): (a) supracoracoideus to the muscle of that name and to
the integument of the breast; (b) thoraci inferiores nerves (10a)--a
complex of nerves from the eighth, ninth, and tenth spinal stems--lead
to the costo-coracoideus muscles and to the anterior part of the
transversus abdominis muscle; (c) the pectoralis (19), a large nerve
leading to the muscle of that name; (d) cutaneus pectoralis (18), fine
branches from the XIth spinal nerve to the integument of the axilla and
the neighboring parts of the breast; (e) coraco-brachialis (22) to the
like named muscle; (f) cutaneus brachii et antebrachii medialis (25 +
42) to the medial side of the integument of the upper and fore arm; (g)
brachialis longus inferior (21), a large nerve that supplies the biceps
and humero-antebrachialis inferior muscles, and then divides into the
medianus and ulnaris inferior nerves; (h) subscapularis (29) to the
like named muscle; (i) scapulo-humeralis profundus (36a) to the like
named muscle; (j) axillaris, a large stem that divides into two main
twigs that lead to the skin of the lateral side of the upper arm, to
the proximal part of the forearm, to the humero-radialis muscle, and to
the deltoides coraco-sternalis muscle; (k) dorsalis scapulæ (posterior)
(31) to the deltoideus scapularis muscle; (1) teres major (29b),
one (alligator) or two (crocodile) middle-sized nerves to the teres
major muscle; (m) latissimi dorsi (29b) to the like named muscle; (n)
brachialis longus superior (radialis) (not shown in Figure 31) to the
extensor side of forearm and the hand.
Of the spinal nerves between the brachial and crural plexuses Bronn
gives no description for the Crocodilia. The most posterior nerve of
the former plexus is the eleventh and the most anterior nerve to take
part in the latter is the twenty-third, so that there are eleven nerves
that are doubtless distributed to the regions not supplied by the two
plexuses.
[Illustration: FIG. 32. CRURAL PLEXUS AND ISCHIADIC PLEXUS OF THE LEFT
SIDE OF A. MISSISSIPPIENSIS. THE NERVE BRANCHES ARE SHOWN AS FAR AS
THEIR ENTRANCE INTO THE MUSCLES. THE CRURAL PLEXUS IS MADE UP OF THE
PRESACRAL STEMS _a_, _b_, _c_. THE OBTURATOR NERVE IS BUILT OF TWO
BRANCHES FROM STEMS A & B. (FROM BRONN, AFTER GADOW.)
_a_, _b_, _c_. presacral nerves.
_α_ & _β_. postsacral nerves.
_s_ = _XXVI_. sacral nerve (26th spinal nerve).
2. to extensor ileo-tibialis muscle.
3. to femoro-tibialis muscle.
4. to ileo-fibularis muscle.
5. to ileo-femoralis muscle.
6. to caudi-ileo-femoralis muscle.
7. caudi-femoralis muscle.
8. to flexor tibialis externus muscle.
9. to flexor tibialis internus muscle.
11. to ischio-femoralis muscle.
13. pubo-ischio-femoralis internus.
14. pubo-ischio-femoralis externus muscle.
15. to pubo-ischio-femoralis posterior muscle.]
The crural-ischial plexuses (Fig. 32) are made up of branches from five
nerves, three presacral (a, b, and c), the sacral (s = xxvi), and one
postsacral (α); the second postsacral shown in the figure apparently
does not enter into the plexus.
The first and second presacrals terminate chiefly in the abdominal and
thigh muscles, though the second sends a large branch to fuse with a
branch from the third to form the large obturator nerve (N. obt.) that
leads to the muscles of the thigh and knee.
The third presacral sends a branch back to fuse with the large sacral
(s = xxvi), and these two, together with a branch from the first
postsacral, form a complicated network that sends numerous branches
to the muscles of the pelvic and femoral regions, to the skin, legs,
and tail, as shown in Figure 32. The large muscles of the tail are
innervated by the regular, metameric nerves of that region, and since
there are usually thirty-nine caudal vertebræ, there are probably about
that many pairs of caudal nerves, although the last few vertebræ and
the muscles of that region are so small it may be that some of the
nerves are lacking.
SPECIAL SENSE ORGANS
It is not possible in a work of this size to give much space to
the discussion of the anatomy of the special sense organs. A few
of the main features will be given here, taken mainly from Bronn’s
_Thierreich_, but for details of structure the reader is referred to
that larger work.
_The Eye._ As might be expected, the Crocodilia have the usual upper
and lower eyelids and the nictitating membrane. Except along their
thickened rims the lids are usually rather faintly pigmented, and near
the thickened border numerous goblet cells are found.
The structure of the upper and lower _lids_ is similar except that in
the former a bony formation is present, as a support to that lid, even
in very young animals. The arrangement of the muscles, which are of
both smooth and striped fibers, and the histological structure cannot
be described here.
The _nictitating membrane_ is strongly developed in the Crocodilia. Its
outer surface is marked by two fairly high folds that are conspicuously
pigmented. The cartilage described in the nictitating membrane of
Lacerta is wanting, according to Bronn, in the Crocodilia.
The glands of the eye are of three types: the lachrymal glands proper,
the Harderian glands, and the conjunctival glands. The _lachrymal
gland_ is small in proportion to the size of the eye. It is an
elongated, almost band-like structure situated in the roof of the
eye-socket, near its border; its long axis lies in an antero-posterior
direction. It is so closely inclosed by and united with connective
tissue that it is difficult to find.
The _Harderian gland_ is much larger than the lachrymal gland proper
and is easily found. It lies in the forward part of the eye-socket
and is of a somewhat three-cornered shape. From its outer and forward
base it sends a short, delicate duct to open between the nictitating
membrane and the eyeball.
The _lachrymal canal_ is well developed in the Crocodilia. Near the
forward angle of the eye, on the inner side of the lower lid, are found
from three to eight tear dots, lying in a row from behind forward.
Each of these dots opens into a small elongated sac. This sac opens
downwards and forwards into a common canal, which canal, at first
narrow but soon widening, extends for a time parallel to the free
border of the eyelid and then enters the opening in the hinder side of
the lachrymal bone. Rathke found none of these tear dots on the upper
eyelid so concluded that the lachrymal fluid could escape only through
the lower lid. This canal, which might correspond to the lachrymal sac
of higher forms, is rather narrow until it enters the lachrymal bone,
then it becomes considerably wider and forms a sort of reservoir that
Rathke calls the “_saccus naso-lachrymalis_.” This reservoir is of
irregular form and opens forwards into the base of the nasal cavity
proper.
The third type of gland mentioned above, the _conjunctival_, is found
on the lower eyelid where the conjunctiva passes from the lid to the
eyeball. The gland is of a “scattered acinose” type.
The usual muscles of the eyeball are found in the Crocodilia. The four
_rectus_ and two _oblique_ muscles have about the usual arrangement and
are attached to the eyeball by very short aponeuroses. The _retractor
oculi_ muscle is only weakly developed. It consists of two separate
bundles which, lying behind the optic nerve, arise from the forward
bony wall of the socket and are inserted on the sclera very near the
optic nerve.
The _eyeball_ consists of the usual layers, including, as might be
expected from the nocturnal habits of the Crocodilia, a typical
_tapetum lucidum_.
In the _sclera_, instead of the bony ring common to the saurians, is
found a well-developed cartilage covered with the fibrous layer of the
sclera; the fibers of this layer are arranged into two more or less
distinct layers.
While not worked out in detail the _cornea_ consists of the usual five
layers.
In the _iris_ the musculature is less developed than in the birds;
Bronn thinks this may be compensated for by the greater development of
the “vascular structures.”
The _pupil_ is a vertical slit.
The _choroid_ is very closely united on the outside with the sclera; on
the inside it is less closely attached to the retina except at the ora
serrata. It consists of an outer fibrous coat, an inner, unstratified
pigmented epithelium derived embryologically from the pigmented layer
of the retina, and the ground substance which is a network of irregular
and very vascular cells.
As in probably all reptiles there is present in the Crocodilia a
vascular pigmented fold of the choroid, the _pecten_, which projects
into the middle of the cavity of the eyeball.
In the _retina_ Bronn describes the following ten layers, which are
those commonly given in other vertebrate retinas: (1) the inner
limiting membrane, (2) optic fiber layer, (3) ganglion cell layer,
(4) inner granular layer, (5) inner nuclear layer, (6) outer granular
layer, (7) outer nuclear layer, (8) outer limiting membrane, (9) cone
layer, (10) pigmented layer. The Crocodilia differ from probably all
other reptiles in having rods as well as cones in the retina. The rods
are more numerous except in the neighborhood of the fovea centralis
where the cones predominate; in the fovea itself only cones are found.
The _lens_ does not show any characteristics unusual enough to warrant
special description.
_The Ear._ The ear is of special interest here because it is in the
Crocodilia that are first found the three distinct regions of the ear
that are seen in the Aves and Mammalia: the external auditory meatus,
the tympanic cavity, and the labyrinth. It is the presence of the
meatus that lifts the Crocodilia above the other Reptilia.
Two strong folds of integument, one above and one below, completely
cover the outer ear and allow it to open as a mere slit on the lateral
surface of the head a little back of the corner of the eye. By lifting
the upper valve one may perceive the lower half of the meatus and
the bottom of the tympanic membrane. The upper valve is the larger
and is sickle shaped; the lower is smaller and more three cornered.
Both spring from the outer surface of the squamosal bone, from its
posterior obtuse angle to its anterior union with the postfrontal.
The lower fold is raised highest behind the corner of the eye and is
lost in the middle of the rima auditoria; by this Hasse indicates the
position of the outer opening of the external auditory meatus. The
form of the _meatus_ may be compared to a wedge whose base is directed
dorso-medio-caudad and whose edge points in a ventro-latero-cephalic
direction; its side walls are either soft or bony; its outer end is
covered by the folds; at its inner end is the tympanic membrane or drum.
The _drum_ is a round, soft, elastic membrane in which a radial
arrangement of its constituent fibers may be seen. It is funnel shaped
from without and above, and the fibers radiate from the apex to which
the columella is attached. The membrane is stretched taut and while
it does not, as in the higher vertebrates, lie in a bony groove, it
possesses around its periphery a strong thickening of circular fibers,
the _annulus tympanicus_, by means of which it is closely united with
the lining membrane of the outer ear passage. The drum is attached
chiefly to the quadrate but in part to the squamosal bone.
The _middle ear_ is divided into an outer part, the _tympanic cavity
proper_, and a part next to the labyrinth, the _recessus cavi tympani_.
Within the tympanic cavity, besides blood-vessels and nerves, is
found the _columella_ with its appendage (found in all Reptilia), the
_recessus scalæ tympani_. The tympanic cavity is formed mainly by the
quadrate, though the exoccipital and squamosal bones take some part.
In outline it might be compared to a truncated, four-sided pyramid,
with its base below, its truncated apex above, and with an anterior, a
posterior, a mesial, and a lateral side.
From the floor of each tympanic cavity a _Eustachian tube_ leads
towards the throat. These tubes unite and connect with the throat by a
single small opening just behind the posterior nares, as shown in the
figures of the skull.
The _semicircular canals_ with their _ampullæ_ lie in the usual
positions as seen in other vertebrates: the anterior vertical,
posterior vertical, and horizontal. The details in structure of the
inner ear cannot be given here. The nervous epithelium is said to have
the same characteristics as in other vertebrates.
CHAPTER V
THE DIGESTIVE SYSTEM
THE ORAL CAVITY
The _mouth_ in the Crocodilia is large, as is well known, and may be
opened very wide. It is bounded anteriorly and laterally by the teeth
of the two jaws; these teeth were described in connection with the
skull. The mucous membrane of the roof of the mouth and of the dorsum
of the tongue, especially the former, exhibits numerous small papillæ
(see page 160), and among these, in the posterior region of the mouth,
are the ducts of mucous glands.
[Illustration: FIG. 33. INTERIOR OF THE MOUTH OF A. MISSISSIPPIENSIS
_f_, transverse fold at the base of the tongue; _v_, _v_, velum
palatinum.]
The _tongue_ extends from just back of the mandibular symphysis to the
glottis. It is attached throughout its entire ventral side except for
a short distance at its tip, so that it may be elevated and depressed
but not protruded. Among the papillæ on its dorsal surface are sense
organs, said to be tactile and gustatory corpuscles (see page 165). The
posterior margin of the tongue is elevated as a transverse fold that
meets a corresponding fold, the _velum palatinum_, from the lower side
of the palate and completely shuts off the mouth from the openings of
the trachea and gullet (Fig. 33). Into this hinder chamber open the
posterior nares, so that the animal can open its mouth under water
without getting water into its trachea; or it may, while holding its
prey in its mouth, come to the surface to breathe, without danger of
letting water into its trachea. The nasal passages, leading from the
nostrils to the posterior nares, are, of course, completely inclosed by
bone, as described in connection with the skull. Ventral to the larynx
and posterior part of the mouth is the large, shield-shaped hyoid
apparatus, Fig. 25, h, also described in connection with the skull.
THE ŒSOPHAGUS