II. In the family of the Crocodilidæ the teeth are usually strong and very unequal in size, and there is always a considerable difference between the anterior and the posterior teeth. The two anterior mandibular teeth are received into pits in the premaxilla; but the canines pass into grooves (which may be converted into fossæ) situated at the junction of the premaxilla and maxilla. The other mandibular teeth are received between the maxillary teeth. The symphysis of the lower jaw does not extend beyond the level of the seventh or the eighth mandibular tooth. The premaxillo-maxillary suture may be either straight or strongly convex backwards. The divided vomers do not appear in the palate. The posterior nares look more or less backwards, and are transversely elongated. The supra-temporal fossæ are always open, and the feet are distinctly webbed. The dorsal scutes are not articulated; and there are no ventral scutes.
Two genera, Crocodilus and Mecistops, are distinguishable in this family.
Genus 4. Crocodilus.
The teeth are always strong and very unequal, the strongest in the upper jaw being the tenth. The mandibular symphysis does not extend beyond the level of the sixth tooth. There are usually six cervical scutes, in two rows, or forming a rhomb, and separated by a distinct interval from the tergal scutes. There are 18 or 19 teeth above, and 15 below, on each side.
1. Crocodilus vulgaris.
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 | 83/4 |
| From the snout to the middle of the canine notch | 23/4 |
| Transverse diameter of snout opposite 10th tooth | 47/8 |
| Long axis of orbit | 21/4 |
| Short axis of orbit | 15/8 |
| Interorbital space opposite the middle of the orbit | 13/4 |
| Anterior edge of the orbit from end of snout | 101/2 |
| Syncipital[3] area in length, about | 21/2 |
| "" in breadth anteriorly | 33/4 |
| """ posteriorly | 4 |
| Supra-temporal fossæ, wide | 7/8 |
| "" long | 11/8 |
| Least width of parietal | 7/16 |
| Total length of mandible | 201/2 |
| Its greatest depth | 3 |
| Length of cervical region (or anterior 8 vertebræ) | 101/2 |
| " dorso-lumbar region | 27 |
| " sacral | 33/4 |
| Length of humerus | 71/2 |
| " ulna | 51/4 |
| " fore foot, extreme length | 6 |
| " femur | 81/2 |
| " tibia | 6 |
| " hind foot, extreme length | 91/4 |
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 53/4 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.
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.