X SKULL 437 



disappear in some of the Alligators, namely in the broad- and 

 short-snouted members, which, having a varied diet, taken from 

 every available group of the animal kingdom, chew their 

 prey. 



The quadrate extends obliquely backwards, and is immovably 

 wedged in and partly fused with the quadrato-jugal, the 

 squamosal, and the lateral occipital wings. Between the latter 

 and the quadrate remains a slit-like canal, well visible from 

 behind, through which passes the continuation into the mandible 

 of the columellar or ossicular chain of the auditory apparatus. 

 Intricate passages, used as additional enlargements of the space of 

 the middle ear, pervade the proximal portions of the quadrate 

 and the roof of the cranium beneath the parietal bridges 

 mentioned above, the two sides communicating with each other. 

 The supra-occipital bone is visible from behind ; its top is covered 

 and partly fused with a continuation of the parietals, which 

 are, like the frontals, fused into an unpaired mass. The 

 occipital condyle is formed entirely by the basi-occipital bone, so 

 far as the articulating facet is concerned, but it is supported on 

 either side by a lamella from the lateral occipitals. 



The two halves of the lower jaw form a symphysis of very 

 variable length. Each half is composed of six bones. (1) The 

 articulare, perforated in its upper, posterior, inner corner by a canal 

 for the reception of the siphonium, a narrow tube of connective 

 tissue, which connects the cavities of the middle ear with the large 

 empty space enclosed within the lower jaw ; (2) the angulare ; 

 (3) the dentary, which alone carries the teeth; (4) the splenial, 

 a long splint-like bone on the surface of the inner or median side 

 of the jaw, of variable length ; (5) the operculare, the counter- 

 part of the splenial on the outer side; (6) the supra-angulare, 

 which forms the dorsal Ijorder of the lower jaw between the 

 dentary and the angulare. 



The teeth, which are more or less conical or compressed 

 laterally, are deeply implanted in separate sockets. They are 

 often shed throughout life, the successors lying on the median 

 side, and with their caps partly fitting into the wide, open roots 

 of the teeth to be expelled. The number of teeth in the pre- 

 maxilla is universally five on either side in recent forms, but in a 

 few species, e.g. Crocodilus niloticus and C. 2)orosns, the second pair 

 is lost with maturity and is not replaced. In the broad-snouted 



