SKELETON OF THE CKOCODILE. THE CRANIUM. 247 



The supra-occipital (fig. 45, 5) is a small bone which 

 takes no part in the formation of the foramen magnum, and is 

 closely united in front with the epi-otic. It is characteristic of 

 Crocodiles that all the bones of the occipital segment have 

 their longer axes placed vertically, and that they scarcely if at 

 all appear on the dorsal surface. 



In front of the occipital segment is the parietal segment. 

 The dorsal and ventral portions of the two segments are in 

 contact with one another, but the lateral portions are widely 

 separated by the interposition of the auditory and suspen- 

 sorial bones. 



The basisphenoid (fig. 45, 12) is an unpaired wedge- 

 shaped bone, united along a deep vertical suture with the basi- 

 occipital. The two bones are, however, partially separated in 

 the mid-ventral line by a foramen, the opening of the median 

 Eustachian canal, which leads into a complicated system of 

 Eustachian passages ultimately communicating with the tym- 

 panic cavity. 



The dorsal surface of the basisphenoid is well seen in a 

 section of the skull, but owing to the way it tapers ventrally, 

 it appears on the ventral surface only as a very narrow strip 

 of bone wedged in between the basi-occipital and pterygoids. 

 In a lateral view it is seen to be drawn out in front into an 

 abruptly truncated process, the rostrum, which forms part of 

 the interorbital septum. On the anterior part of the dorsal 

 surface is a deep pit, the pituitary fossa or sella turcica, 

 at the base of which are a pair of foramina, through which 

 the carotid arteries pass. Dorso-laterally the basisphenoid 

 articulates with the alisphenoids. 



The alisphenoids (fig. 45, 13) are a pair of irregular bones 

 which arise from the basisphenoid antero-laterally, and are 

 united dorsally with the parietal, frontal, and postfrontals. 

 They bound most of the anterior part of the brain case, 

 and each presents on its inner face a deep concavity which 

 lodges the cerebral hemisphere of its side. Viewed from 



