=Innominate Bones. Ossa innominata.= (=Os coxæ BNA=) (Figs. 54 and
55).--The two innominate bones articulate with the sacrum and extend
thence caudoventrad and finally turn mediad and unite in the middle
line, forming the =symphysis pubis=. They thus form an arch, =the pelvic
arch=, =pelvic girdle= or =pelvis=, which is closed dorsad by the
sacrum.
In the middle of the lateral surface of each bone is a hemispherical
depression, the =acetabulum= (Fig. 55, _d_), which receives the head of
the femur.
[Illustration: FIG. 54.--INNOMINATE BONE OF KITTEN, VENTROLATERAL
VIEW.
_I_, ilium; _II_, ischium; _III_, pubis; _IV_, acetabular bone. _a_,
acetabulum; _b_, obturator foramen.]
In the kitten each innominate bone is composed of three principal parts
united by sutures (Fig. 54). From the sacrum to the acetabulum is a
single bar, the =ilium= (_I_). Caudad of the acetabulum are two bars.
The dorsal one of these is the =ischium= (_II_), and the ventral one is
the =pubis= (_III_). The ischium enters into the formation of the
acetabulum (_a_), but the pubis does not. The two bones, however, are in
contact at the ventral edge of the acetabulum. From this point they
diverge, but unite with one another again near the middle line and thus
enclose an oval foramen, the =obturator foramen= (_b_). Wedged between
the ilium, ischium, and pubis at their point of junction and helping to
form the acetabulum is a small irregular bone, the =acetabular bone=
(_IV_). In the adult cat these four parts are united into a single bone
which is nevertheless usually described, ignoring the acetabular piece,
as made up of ilium (Fig. 55, _I_), ischium (_II_), and pubis (_III_).
[Illustration: FIG. 55.--INNOMINATE BONE OF ADULT CAT, VENTROLATERAL
VIEW.
_I_, ilium; _II_, ischium; _III_, pubis. _a_, crest of the ilium; _b_,
posterior inferior spine; _c_, great sciatic notch; _d_, acetabulum;
_d′_, incisura acetabuli; _e_, spine of the ischium; _f_, lesser
sciatic notch; _g_, tuberosity of the ischium; _h_, ramus of the
ischium; _i_, ramus of the pubis; _j_, obturator foramen; _k_, pubic
tubercle; _l_, iliopectineal line; _l′_, ilio-pectineal eminence; _m_,
anterior superior process.]
The =ilium= (_I_) is somewhat contracted at the middle and broader at
its ends. One end enters into the acetabulum (Fig. 55, _d_) and forms
about one-fifth the articular surface. This end is also the thickest
part of the bone. The lateral surface of the ilium is concave for the
attachment of muscles. The medial surface is smooth over its acetabular
half and rough over its sacral half. The rough portion is marked at its
junction with the smooth portion by the ear-shaped =auricular
impression= by which the bone articulates directly with the sacrum. The
caudal half of that part of the medial surface craniad of the auricular
impression gives attachment to the ilio-sacral ligaments which bind the
ilium to the sacrum. The dorsal border is straight at its cranial end
and concave and rounded at its caudal end. Between the two portions and
at the dorsal edge of the auricular surface is a protuberance
corresponding to the =posterior inferior spine= (Fig. 55, _b_) of the
human ilium. The concavity of the dorsal border (_c_) corresponds to the
great sciatic notch of the human ilium. At its caudal end is the short
=spine of the ischium= (_e_), which is not a part of the ilium. The
ventral border of the ilium is broad caudad, becoming narrower craniad.
The lateral margin of the ventral border is continued to a tuberosity at
the edge of the acetabulum; its medial margin is called the
=iliopectineal line= (_l_) and extends on the pubis to the symphysis. An
eminence, the =iliopectineal eminence= (_l′_), on the iliopectineal
line, lies opposite to the acetabulum at about the junction of the ilium
and pubis. The cranial end of the bone is thickened, forming the =crest=
(_a_) of the ilium. At the junction of the crest with the ventral border
is a projection, the =anterior superior process= (_m_) of human anatomy.
The =pubis= (_III_) (including the acetabular bone) enters into the
formation of the acetabulum (_d_) constituting about one-sixth the
circumference, but less than one-sixth its area. It may be described as
a flat, curved bone, contracted at the middle and expanded at the ends.
The dorsal end enters into the acetabulum; the ventral end unites with
the opposite bone at the symphysis pubis and sends caudad a projection,
the =ramus= (_i_) of the pubis, which unites with the ramus of the
opposite bone to form about two-thirds of the entire symphysis. At the
sides of the symphysis a slightly marked angle projects craniad from
each of the pubic bones; these two together constitute the =pubic
tubercle= (_k_), for the origin of the rectus abdominis muscle. The
surfaces of the ramus are smooth. One of its borders is concave and
enters into the formation of the obturator foramen (_j_). Another of its
borders is the iliopectineal line (_l_). Its third border is rough for
the symphysis.
The =ischium= (_II_) has the form of a triangular prism contracted at
the middle. Its cranial end forms nearly two-thirds of the acetabulum.
Its caudal end bears dorsad a rough thickening, the =tuberosity= of the
ischium (_g_). From the caudal half of the ventral border of the bone a
sickle-shaped process, the =ramus= (_h_) of the ischium, curves
medioventrad and then craniad and joins the ramus of the pubis. Its
medial border is rough and enters into the symphysis, forming the caudal
one-third. The lateral angle of the bone is rounded. Its dorsal angle is
marked near the cranial end by the =spine= (_e_) of the ischium. The
concavity between this spine and the tuberosity corresponds to the
=lesser sciatic notch= (_f_) of human anatomy.
The acetabulum (_d_) is cup-shaped. The ventral one-sixth of its border
is deficient and a broad groove extends from the deficiency to the
bottom of the cup. The deficiency, =incisura acetabuli=, or =acetabular
notch= (_d′_), is closed naturally by a ligament, and the groove gives
origin to the ligament (ligamentum teres) which attaches the head of the
femur.
[Illustration: FIG. 56.--LEFT FEMUR, VENTRAL SIDE.
_a_, head; _b_, neck; _c_, depression for round ligament; _d_, great
trochanter; _e_, trochanteric fossa; _f_, intertrochanteric line; _g_,
lesser trochanter; _h_, linea aspera; _i_, medial condyle; _j_,
lateral condyle; _k_, intercondyloid fossa; _l_, lateral epicondyle.]
=Femur= (Fig. 56).--The femur is the proximal bone of the posterior
extremity. It consists of enlarged proximal and distal ends connected by
a nearly cylindrical shaft. The proximal end presents on its medial side
a hemispherical =head= (_a_) which fits into the acetabulum. It is
supported by a =neck= (_b_) which is contracted near the head and
expanded dorsoventrally where it joins the remainder of the bone. The
medial surface of the head presents near its ventral border a depression
(_c_) for the insertion of the round ligament of the femur. Ventrad the
articular surface of the head extends as an acute projection onto the
shaft, so that the whole articular surface appears somewhat pear-shaped.
On the lateral side of the proximal end opposite the head is a
projecting mass, the =great trochanter= (_d_), forming the end of the
shaft. On the medial side of the great trochanter at its junction with
the neck is a deep fossa, the =trochanteric= fossa or =digital= fossa
(_e_) for the insertion of muscles. From the ventral surface of the
great trochanter a ridge, the =intertrochanteric= line (_f_), is
continued distad, ending in a pyramidal projection, the =lesser
trochanter= (_g_), which serves for the insertion of muscles. A second
ridge is continued to the lesser trochanter from the neck. A slight but
well-marked ridge, the =spiral= ridge or line, runs round two sides of
the neck parallel to the second ridge.
The shaft is nearly straight and cylindrical. A rough line is continued
along its ventral surface from the lesser trochanter, and a similar line
along its lateral surface from the greater trochanter; these unite
ventrad to form the =linea aspera= (_h_). On its ventral surface is a
nutrient foramen, directed proximad.
The shaft gradually widens distad and ends in two =condyles= (_i_ and
_j_) which are continuous dorsad but separated ventrad by a deep notch,
the =intercondyloid fossa= (_k_). The distal surface of the shaft and
condyles is articular. This articular surface is larger on the lateral
condyle (_j_). The part of the articular surface on the end of the shaft
(=patellar surface=) is for the patella; that part of it on the condyles
and separated by the notch is for the tibia.
On the lateral surface of the lateral condyle is a slight prominence,
the lateral epicondyle (_l_), and on the medial surface of the medial
condyle is another prominence, the medial epicondyle; both are for the
attachment of ligaments.
=Patella= (Fig. 1, _r_).--The patella is a small flat bone with a
pear-shaped outline, having its apex distad. It lies against the
articular surface at the lower end of the shaft of the femur. It thus
covers the knee-joint. The inner surface is smooth and convex from side
to side, but concave in a proximodistal line. It fits against the lower
end of the femur. Its outer surface is rough and concave. It is a
sesamoid bone inserted in the tendon of the quadriceps femoris muscle.
Three other sesamoid bones are found in the region of the knee (see Fig.
61, p. 89). Two are in the tendons of the gastrocnemius muscle, proximad
of the two condyles of the femur. The third is in the tendon of the
popliteus muscle, just laterad of the lateral condyle of the femur.
[Illustration: FIG. 57.--TIBIA AND FIBULA OF LEFT LEG, DORSAL VIEW.
_I_, tibia; _II_, fibula. _a_, medial condyle of the tibia; _b_,
lateral condyle; _c_, spine of the tibia; _d_, crest of the tibia;
_e_, tubercle for attachment of the patellar ligament; _f_, medial
malleolus; _g_, projection of dorsal surface of the tibia; _h_, head
of fibula; _i_, lateral malleolus.]
=Tibia= (_I_, Fig. 57).--The tibia is the longer of the two bones of the
leg between the knee and the ankle, and is the longest bone of the body.
It has a triangular shaft and enlarged proximal and distal ends.
The proximal end is curved ventrad and projects into two prominences,
the =tuberosities=, on either side. Each tuberosity bears on its
proximal end an articular facet for the condyles of the femur; these are
known respectively as the =lateral= and =medial condyles= (_a_ and _b_)
of the tibia. The condyles are oval, convex dorsoventrad, and concave
from side to side. The two condyles are separated at the middle of their
contiguous margins by a bicuspid projection, the =spine= of the tibia
(_c_). They are continuous dorsad, but separated ventrad by a deep notch
between the tuberosities, the =popliteal= notch. On the distal side of
the lateral condyle is an elongated facet for the proximal end of the
fibula.
The shaft is triangular, smallest at about its middle and enlarged at
both ends. It presents dorsal, medial, and lateral borders, and medial,
lateral, and ventral surfaces. The lateral surface is concave proximad.
The medial surface is convex. The two are continuous at the distal end.
At their proximal ends the border separating them is raised into a
prominent ridge, the =crest= (_d_) of the tibia, the proximal end of
which contributes to increase the proximal surface of the bone, and
presents an oblong tubercle (_e_) for the insertion of the =ligamentum
patellæ= (ligament of the quadriceps femoris muscle). The ventral
surface is concave proximad where it abuts upon the tuberosities. Its
proximal half is crossed by two rough parallel lines, the distal one of
which crosses in a spiral course from the lateral to the medial border;
near its beginning is a nutrient foramen.
The distal end extends farther distad on its medial side. The extension
is the =medial malleolus= (_f_). The malleolus presents two grooves on
its medial surface for the tendons of muscles. On the lateral side of
the distal end is an oblique triangular facet for the distal end of the
fibula. The ventral surface of the distal end presents an oblique border
which passes from the apex of the malleolus proximolaterad. The dorsal
surface extends into a V-shaped projection (_g_) between the malleolus
and the fibular facet. The distal end presents an oblique ridge running
from the apex of the V-shaped extension of the dorsal surface to near
the base of the medial malleolus. The ridge and the concavities on
either side of it, the medial one of which is deeper, fit against the
proximal trochlear surface of the astragalus.
=Fibula= (_II_, Fig. 57).--The fibula lies at the lateral side of the
tibia in the shank. It is a slender triangular bone with enlarged
proximal and distal ends.
The proximal end or head (_h_) is flattened. It bears a facet on its
proximomedial surface for articulation with the tibia, and is
longitudinally grooved on the outer surface.
The shaft has a very sharp medial border. This border is turned toward
the tibia and gives attachment to the interosseous membrane, which runs
between the tibia and fibula.
The distal end is expanded to form the =lateral malleolus= (_i_). This
bears a facet on the proximal portion of its medial surface near its
dorsal margin, for the tibia, and distad of this is a second facet for
the astragalus. The ventral and lateral surfaces are grooved for
tendons.
=Tarsus= (Fig. 58).--The tarsus consists of seven bones. The longest of
these, lying on the lateral side of the foot and forming the support of
the heel, is the =calcaneus= or =os calcis= (_a_). It articulates distad
with a bone, the =cuboid= (_c_), which bears the fourth and fifth
metatarsals. Lying between the calcaneus and the tibia is the
=astragalus= or =talus= (_b_), the distal end of which articulates with
the boat-shaped =navicular= or =scaphoid= (_d_). The scaphoid bears on
its distal surface the three cuneiform bones, lateral (_e_), medial
(_g_), and intermediate, bearing the rudiment of the first metatarsal
and the second and third metatarsals.
_Astragalus._ (_Talus BNA_) (Fig. 58, _b_).--The astragalus may be
divided into body, neck, and head. The body is marked on its proximal
surface by a deep pulley-like groove for the articulation with the
distal end of the tibia, and on its lateral and medial surfaces by
curved facets for articulation with the malleoli of the tibia and
fibula. This entire surface for articulation with the bones of the leg
is known as the trochlea. The lower surface is marked by two facets
separated by a groove; these are for articulation with corresponding
facets on the calcaneus. Distally the bone contracts to form the =neck=
and enlarges at the end, forming the =head=, which is smooth on its
distal surface for articulation with the navicular or scaphoid.
_Calcaneus_ (Fig. 58, _a_, and Fig. 59).--The calcaneus (os calcis) is
the largest bone of the foot and forms the heel. It is two or three
times as long as broad and has six surfaces: dorsal, ventral, medial,
lateral, proximal, and distal. The proximal one-half of the dorsal
surface (Fig. 59) is smooth, while the distal half is broadened and
bears two facets which are separated by a groove. These articulate with
the corresponding facets on the astragalus. The medial facet is borne on
a projection of the bone, the sustentaculum tali (_c_). Distad of the
facets the surface is rough. The ventral surface is smooth. The proximal
end (_b_) is grooved for the tendon of Achilles. The lateral surface is
smooth and marked by a grooved tubercle, the =peroneal tubercle= (_d_),
near the distal end. The medial surface is marked by part of the
articular facet for the astragalus, and also by the grooved
sustentaculum tali. The distal end (_a_) articulates with the cuboid.
[Illustration: FIG. 58.--TARSUS, METATARSUS, AND PHALANGES OF LEFT
FOOT, VENTRAL VIEW.
_a_, calcaneus; _b_, astragalus; _c_, cuboid; _d_, scaphoid; _e_,
lateral cuneiform; _g_, medial cuneiform; _h_, peroneal groove, for
the tendon of the peroneus longus muscle; _i_, proximal phalanges;
_j_, second row of phalanges; _k_, distal phalanges; _l_, sesamoid
bones. 1, rudimentary first (medial) metatarsal; 2, 3, 4, 5, the other
metatarsals.]
[Illustration: FIG. 59.--CALCANEUS OF RIGHT FOOT, DORSAL VIEW.
_a_, distal facet for cuboid; _b_, proximal end with groove for tendon
of Achilles; _c_, sustentaculum tali; _d_, peroneal tubercle.]
_Cuboid._ _Os cuboideum_ (Fig. 58, _c_).--The cuboid has somewhat the
form of a cube and articulates by its proximal end with the calcaneus
(_a_), and by its distal end with the fourth and fifth metatarsals. Its
medial surface articulates with the scaphoid (_d_) and lateral cuneiform
(_e_). The ventral surface is marked near its distal end by an oblique
ridge, distad of which is a deep groove, the peroneal groove (_h_), for
the tendon of the peroneus longus muscle.
_Scaphoid._ (_Os naviculare pedis BNA_) (Fig. 58, _d_).--The scaphoid is
a boat-shaped bone. Its proximal surface is marked by a concave facet
for the head of the astragalus (_b_), and its distal surface has three
facets for the lateral (_e_), intermediate and medial (_g_) cuneiform
bones. At the junction of the ventral with the medial surface is a
prominent tubercle. The lateral surface bears two linear facets for
articulation with the calcaneus (_a_) and cuboid (_c_).
_Lateral Cuneiform._ _Ectocuneiform._ _Os cuneiforme tertium BNA_ (Fig.
58, _e_).--The lateral cuneiform is a wedge-shaped bone with a hooked
process extending from the ventral sharp angle of the bone. It
articulates by its proximal end with the scaphoid (_d_), and by its
distal end with the third metatarsal. The medial surface bears near its
distal end two facets for the second metatarsal, and on its proximal end
a facet for the intermediate cuneiform. The caudal surface has a facet
on its proximal end for the cuboid (_c_).
_Intermediate Cuneiform._ _Mesocuneiform._ _Os cuneiforme secundum
BNA._--The intermediate cuneiform is small and wedge-shaped, with the
base of the wedge dorsad. It lies between the lateral cuneiform and the
medial cuneiform, articulates by its proximal end with the middle facet
of the scaphoid, and bears on its distal end the second metatarsal. It
is not visible in ventral view.
_Medial Cuneiform._ _Entocuneiform._ _Os cuneiforme primum BNA_ (Fig.
58, _g_).--The medial cuneiform lies on the medial side of the foot. It
is a flat triangular bone about twice as long as broad, and broader at
its proximal end than at the distal end. It bears on its distal end the
rudimentary first metatarsal. The proximal end is oblique and bears a
concave facet for the lateral distal facet of the scaphoid (_d_). The
lateral surface has a concave facet at its proximal end for the
intermediate cuneiform, while the distal portion is applied against the
medial surface of the second metatarsal.
=Bones of the Foot or Pes= (Fig. 58).--_Metatarsals._ _Metatarsus_ (Fig.
58, 1-5).--The metatarsals are five in number. They bear a close
resemblance to the metacarpals, but they may be distinguished by their
bases.
The _first_ metacarpal (1) is rudimentary and conical. Its base has a
facet for the distal end of the medial cuneiform (_g_), while the outer
surface fits into a depression on the inner surface of the base of the
second metatarsal.
The _second_ (2). The proximal surface of the base is triangular,
corresponding to the distal end of the intermediate cuneiform. The
medial surface is marked by two concavities, one along the proximal
border for the distal end of the medial cuneiform, and one distad of
this for the first metatarsal. The lateral surface bears on the
proximal margin an oblique triangular facet dorsad and a similar facet
ventrad, both for the lateral cuneiform (_e_). Distad of these facets is
a rough ridge.
The _third_ (3). The proximal end of its base is a triangular facet with
the apex directed ventrad and the sides excavated. It is for the distal
end of the lateral cuneiform (_e_). Its medial surface presents a
depression which receives the ridge of the second metatarsal. On the
lateral surface a short distance distad of the proximal border is a
triangular concave facet, and near the proximal border ventrad a second
concave facet. Both are for the fourth metatarsal.
The _fourth_ (4). The proximal end is convex, notched medially and
facetted for the cuboid (_c_). Its medial surface bears dorsad, a short
distance from its proximal end, a smooth tubercle, and ventrad a small
convex facet. Both articulate with facets on the lateral surface of the
third metatarsal. The lateral surface has a sinuous facet along its
dorsal border, and ventrad of this a depression. There is a second facet
along the ventral border. Both facets are for the fifth metatarsal, and
the depression is for ligaments.
The _fifth_ (5) has its base flattened and expanded so as to be
wedge-shaped, with the apex of the wedge directed proximad. Its dorsal
end extends into a tubercle. It thus presents only lateral and medial
surfaces. The medial surface shows two tubercles, one distad of the
other. The distal tubercle and the distal half of the proximal tubercle
are facetted and fit into the sinuous facet on the fourth metatarsal. A
narrow facet on the ventral border of the surface articulates with the
facet on the ventral border of the lateral surface of the fourth
metatarsal. The proximal half of the distal tubercle is facetted for the
cuboid (_c_). The lateral surface is smooth, non-articular, and
obliquely grooved.
_Phalanges_ (Fig. 58, _i_, _j_, _k_).--There are three phalanges in each
of the four digits, and these are almost identical with those described
for the manus.
_Sesamoid Bones._ _Ossa sesamoidea_ (Fig. 58, _l_).--The sesamoid bones
are found at the joints between the metatarsals and phalanges, and are
in all respects like those of the manus.