ANATOMY OF VERTEBRATES. 



145 



The locomotive extremity, fig. 92, 53-57, is the diverging ap- 

 pendage of the arch, under one of its numerous modes and grades 

 of developement. 



Coadjusted as the above-defined vertebral elements are in the 

 skull of the Crocodile, they compose such a whole as is represented 

 in fig. 95. Each temporal fossa is circumscribed externally by 

 two horizontal bony arches ; the upper one formed by the post- 

 frontal, 12, and mastoid, 8 ; the lower one by the malar, 26, and 

 scpaamosal, 27 : the tympanic, 28, and mastoid, 8, bound the 

 fossa behind : the coarticulated processes from the postfrontal and 

 malar form a partial division between the fossa and the orbit in 



95 



~4 



22 





32 



26 



29 



Skull of Crocodile 



front. The orbit is circumscribed by these bones, with the frontal, 

 n, prefrontal, 14, and lacrymal, b. A superorbital or palpebral 

 derm-ossicle strengthens the upper eyelid. The external nostril, 

 single and advanced in Crocodilia, is surrounded sometimes, as in 

 Gavials, by the premaxillaries, 22 ; sometimes, as in fig. 95, admit- 

 ting also the points of the nasals, 15. The internal nostril opens far 

 back, beneath the occiput, fig. 98 c, n, and is exclusively surrounded 

 by the pterygoids, 24: its plane is horizontal in Gavials and some 

 Alligators ; but is more or less oblique, looking backward, in 

 Crocodiles. Behind and above it are the median and lateral 

 Eustachian bony outlets, from which the membranous continua- 

 tions of the tubes converge and unite in the single valvular aper- 

 ture on the soft palate. 1 The vast extent of the bony roof of the 



1 clxxii., pi. xii. fig. 5. This paper may be referred to for other cranial foramina, 

 and for the details of the complex bony structure of the median and lateral 

 VOL. I. L 



