DEVELOPMENT OP THE SKULL IN THE CKOCODILIA. 301 



The chondrocranium is better developed than in any existing order of Reptiles and 

 in any kind of Birds ; that of the African Ostrich {Struthio) comes nearest to it. The 

 best kind for comparison with it, below, is that of the Skate ; if compared with that 

 which is above, it is seen to come very near to that of any ordinary Mammal at the 

 same stage, e. g. the Pig ; but the auditory labyrinth is in the condition in which it 

 is found in an embryo of the Pig three quarters of an inch in length. The occipital 

 condyle, however, in the Crocodile is single, and not double as in the Skate, below, and 

 the Mammal, above ; but the development of the occipital arch, the impaction of the 

 large auditory capsules, the continuity of the upper part of the wings of the sphenoid 

 with the nasal and auditory capsules, and the development of the whole basis cranii 

 (crested in the prepituitary region, and carrying the long nasal capsules) — all these 

 things are like what we see in the Mammalia, except that the top of the alisphenoid is 

 not free. The hard palate of this type is equal to what we see in such a mammal as 

 Myrmeco])haga, where it has its fullest growth, the pterygoids continuing the floor. 



As we dissect the arrested and highly modified hyoid arch, we seem to be examining 

 a creature very different from a Mammal ; the basal part of the stapes is not distinct as in 

 the Frog, and the parts which are specialized to auditory functions are normally Sauro- 

 psidan, but have an additional segment, the siipr ((stapedial. Yet, below, the basihyo- 

 branchial plate and the hinder cornua are very much like what we see even in Man. 



But the mandibular arch is as far as can be from that of a Mammal ; here it is at 

 its utmost development, the lower jaw of the oviparous type in its culmination. 



In the Mammal, on the other hand, the arrest of this as well as of the other visceral 

 arches — in all the " Amniota " the hindermost arches are suppressed — reveals a great gulf 

 between them and the Sauropsida. This is correlated with the fine and perfect coiling 

 of the cochlea ; to that highest development of the auditory labyrinth there is superadded, 

 in Mammals, an additional arrested and specialized visceral arch in the outer (tympanic) 

 part of the organ. 



In the early stages the mandibular suspensorium of the Crocodile is extremely like 

 that of the more generalized Selachians — Notidanus, Cestracion — ^just as the hyoid arch 

 is like that of the Skate, or even of the Chimcera. 



But the fore part of the pterygo-quadrate bar, or working upper jaw, is arrested in 

 the Crocodile, whilst the " otic process " is inordinately large. 



A separate rudiment of the Shark's huge, projecting upper jaw (" pterygoid carti- 

 lage ") appears, as in Siredon, below, and the Passerine birds, above ; and so also does 

 a remnant of the great coronoid crest of Selachians and Ganoids reappear in the lower 

 jaw of the Crocodile. 



Here, in spite of the strong fixation of the quadrate suspensorium, the lower jaw is 

 separated by it from the skull in the squamosal (or temporal) region ; whereas in 

 mammals the overdeveloped " dentary " bone reaches up to the squamosal, and articu- 

 lates with it, aborting the simple single quadrato-Meckelian rod within. 



