As Cuvier has remarked, it is extremely difficult to find good
distinctive characters for all the species of this genus. My first
difficulty was to ascertain the precise characters of that species which
has been misnamed _vulgaris_, inasmuch as I could find neither in the
British Museum, nor in the Museum of the Royal College of Surgeons, any
_authentic_ skeleton or skull of this, the so-called Nilotic Crocodile.
This difficulty subsisted up to the time that the chief statements
contained in the present essay were laid before the Linnean Society; but
since then I have been enabled, by Dr. Gray's permission, to examine the
skull of a small stuffed specimen, brought to this country from Egypt
by Sir Gardner Wilkinson, and to study the splendid entire skeleton of
a _Crocodilus vulgaris_ in the Christchurch Museum at Oxford, presented
to that Institution by the gentlemen who shot it on the Nile, and set
up with great care under the auspices of my friend Dr. Rolleston, Lee's
Reader in Anatomy and Curator of the Museum. Fortunately the entire
skin has been preserved; so that this is the most complete record of
the hard parts of any individual crocodile with which I am acquainted,
besides being, so far as I am aware, the only authentic entire skeleton
of _Crocodilus vulgaris_ in this country. I subjoin the chief points
of interest which I noted in my brief examination of this valuable
specimen:--
Inches.
The total length of the skeleton is 114
" " " skull 16
Between the outer edges of the posterior ends of
the quadrate bones 8-3/4
From the snout to the middle of the canine notch 2-3/4
Transverse diameter of snout opposite 10th tooth 4-7/8
Long axis of orbit 2-1/4
Short axis of orbit 1-5/8
Interorbital space opposite the middle of the orbit 1-3/4
Anterior edge of the orbit from end of snout 10-1/2
Syncipital[3] area in length, about 2-1/2
" " in breadth anteriorly 3-3/4
" " " posteriorly 4
Supra-temporal fossæ, wide 7/8
" " long 1-1/8
Least width of parietal 7/16
Total length of mandible 20-1/2
Its greatest depth 3
Length of cervical region (or anterior 8 vertebræ) 10-1/2
" dorso-lumbar region 27
" sacral " 3-3/4
Length of humerus 7-1/2
" ulna 5-1/4
" fore foot, extreme length 6
" femur 8-1/2
" tibia 6
" hind foot, extreme length 9-1/4
From the above measurements it will be seen that the skull is somewhat
slender. Behind the canine groove it widens to the tenth tooth, which
is 5-3/4 inches behind the end of the snout. It retains about the
same diameter to the twelfth tooth, and then slowly widens again,--a
sudden increase in size, to the extent of half-an-inch, taking place
opposite the posterior margin of the orbit, owing to the flanging-out
of the jugal. On the whole, however, there is a slow and even increase
in breadth, from the canine groove to the ends of the ossa quadrata.
The nasal aperture is pyriform, its wider end being forwards, and its
narrow posterior extremity, into which the pointed ends of the nasal
bones project, attaining the level of the first tooth behind the canine
groove.
[3] By this term I denote that squarish flat area bounded by
the postfrontal and squamosal bones laterally, by the occiput
posteriorly, and by a line joining the outer angles of the
postfrontals anteriorly.
On the left side there is only a pit for the reception of the
anterior mandibular tooth, while on the right side this pit is
converted into a complete foramen. On the upper face of the skull, the
premaxillo-maxillary suture runs vertically upwards through the canine
groove, and then passes obliquely backwards to a point 5 inches behind
the end of the snout. The anterior part of this suture lies in a strong
ridge, which is continued downwards and forwards on the premaxilla to
the level of the fifth tooth, a groove separating it from the margin
of the nasal aperture. Posteriorly this ridge dies away, but a curved
irregular elevation, convex inwards, arises opposite the tenth tooth. It
is wholly confined to the maxilla, not extending on to the nasals.
There is a distinct, rough, irregular elevation, bounded on its
outer side by a sharp groove, which extends back to the orbit, on
the lachrymal bone. The profile of the skull is convex as far as the
posterior boundary of the nostril, and very slightly concave from that
point as far as the twelfth tooth. It then passes back as a straight,
slightly ascending line, only interrupted by the lachrymal ridge, to
the margin of the occiput. The inferior margin of the maxilla is convex
downwards as far as the canine groove, whose lower end is indicated by
a deep sinuation. It then becomes convex again, the crown of the curve
being at the ninth and tenth teeth, and its posterior end sweeping into
a concavity whose summit is at the twelfth tooth. Behind this the edge
of the maxilla is only slightly convex. The inferior contour of the
jugal bone is very concave; but the articular end of the quadrate bone
descends to the level of the edge of the ninth alveolus.
The orbits have a sort of heart-shape, their apices being turned
forwards, and their more convex sides inwards.
The supra-temporal fossæ are half-moon-shaped, their straight sides
being external and so inclined that, if prolonged, they would decussate
upon a line joining the anterior margins of the orbits.
On the palatine surface of the skull, the premaxillo-maxillary suture
runs backwards from the canine groove, as far as the level of the middle
of the second alveolus behind the groove (or that of the seventh tooth),
which point it reaches at about the junction of the middle with the
inner third of the palatine plate of the maxilla. The suture then turns
abruptly forwards until it reaches the level of the anterior margin of
the alveolus of the sixth tooth, when it bends suddenly inwards to meet
its fellow. The whole suture, therefore, has the form of a W. The vomers
are completely hidden.
The posterior nares look downwards and backwards; their aperture is,
from the incompleteness of the septum, single, and has a transversely
elongated crescentic form. It measures 1-1/8 inch in width by
3/8ths antero-posteriorly. The basi-sphenoid is seen for about
1/8th of an inch on the base of the skull behind it, bounding the
sides of the eustachian tube. The dental formula is 18-18/15-15.
The fourth and tenth teeth are largest in the upper jaw, the first and
fourth in the lower. The eight posterior teeth on each side in the upper
jaw, and the five posterior in the lower, have a marked constriction
between the short crown and the fang of the tooth. There are deep
interdental pits for the reception of the mandibular teeth between the
third and fourth, and fourth and fifth teeth above, and between the
succeeding teeth from the sixth to the thirteenth.
The hyoidean cornua are very strong curved bones, the chord of whose arc
measures 3-1/2 inches. They are concave inwards, convex outwards,
concave posteriorly, convex anteriorly; they are flattened from side to
side below, but they end above in subcylindrical styloid extremities.
In the ninth vertebra the neurocentral suture passes just above the
base of the parapophysis; it traverses the parapophysis in the tenth
and eleventh vertebræ, while in the twelfth the parapophysis suddenly
rises to the root of the diapophysis, and the suture lies far below
it. The centra of the dorsal vertebræ, as far as the thirteenth
inclusive, have hypapophyses. The diapophyses of the ninth vertebra pass
almost horizontally outwards, but are a good deal inclined backwards.
In the succeeding vertebræ up to the fourteenth or fifteenth, the
diapophyses are, in addition, inclined upwards, the upward inclination
being most marked in the tenth, eleventh and twelfth vertebræ. From
the fifteenth vertebra onwards, the transverse processes pass almost
directly outwards, without either upward or backward inclination. The
span of the transverse processes is greatest in the eighteenth and
nineteenth vertebræ, in which the distance between the extremities of
these processes is 7-1/4 inches, a length about equal to that of the
longest vertebral rib.
The rib of the ninth vertebra is terminated by a single long and slender
semicartilaginous process which does not unite with the sternum.
Each of the vertebral ribs from the tenth to the seventeenth vertebræ
inclusively, on the other hand, is united with the sternum, or its
continuation, by two such semicartilaginous costal elements, which
may be respectively termed sternal and lateral. The sternal elements
of the ribs of the tenth and eleventh vertebræ are united with the
sternum proper; those of the next five vertebræ are connected with its
median backward prolongation, while those of the seventeenth vertebra
are attached to the processes into which this prolongation divides
posteriorly.
The sternal costal elements are very broad and flat, and though the
lateral ones are less so, they are wide and expanded. The lateral costal
pieces of the eleventh to the sixteenth vertebræ inclusively, give
attachment to very large and flat, triangular, _processus uncinati_.
Those of the twelfth are 3-3/4 inches long and 1-3/8 inch wide at
their widest part. The transverse processes of the twentieth vertebra
bear rudimentary ribs. The centrum of the thirteenth vertebra is
1-3/4 inch long, and the vertebra is 3-3/4 inches high from the
lower edge of the centrum to the summit of the neural spine. The centra
of the vertebræ retain nearly the same length to the twentieth caudal;
but behind this vertebra they are shorter, as are the anterior dorsal
vertebræ. The first caudal vertebra is provided with two styliform
bones, which represent the chevron bones of the other caudal vertebræ,
but are not united below.
The dorsal scutes have the arrangement which his often been described.
They are separated (except perhaps the median rows) by integumentary
spaces, neither overlapping nor uniting by sutures; and there are no
ventral scutes.
Among the osteological characters which have been detailed, the
peculiarities of the tergal armour, the proportions of the skull,
combined with the characters of the ridges upon its surface, and the
form of the premaxillo-maxillary suture amply suffice to diagnose this
species. Even in the small skull, only 5-1/2 inches long, lent to
me by Dr. Gray, the characteristic features of the species are well
exhibited, although age appears to give rise to many differences. Thus
the posterior margin of the external nostrils does not extend so far
back as in the adult, and the facial is smaller in proportion to the
syncipital region, whose anterior and posterior transverse dimensions
are very nearly equal. The orbits are proportionally larger, the
interorbital space more excavated; and the outer straight margins of
the supra-temporal fossæ are parallel with the longitudinal axis of the
skull. Still more important differences are visible on the palatine
face of the skull. The premaxillo-maxillary suture reaches back, indeed,
to the line of the seventh tooth; but it forms an even curve whose
summit is in the middle line. The aperture of the posterior nares,
again, has a totally different form from that which it assumes in the
adult. It is somewhat heart-shaped, with its apex forwards, measures
1/4 inch long by 3/16ths at broadest, and looks altogether
downwards, while its anterior margin is situated far more forward in the
palate than that of the adult.