The Skeleton . 67 



The basioccipital (14) is seen projecting caudad 

 as the single occipital condyle; it will be described 

 in connection with the posterior aspect of the skull. 



The jugal (5), qiiadraiojugal (12), and quadrate 

 (8) may all be seen from this view. The first two 

 have been sufficiently described in connection with 

 the dorsal aspect ; the last will be further described 

 in connection with the lateral aspect. 



Just caudad to the posterior nares is a small 

 opening, the unpaired Eustachian canal (eu). 



The Lateral Aspect (Fig. 21). As will be seen by 

 the figure, practically all of the bones visible in this 

 view have already been described, except those of 

 the mandible, which will be described separately. 

 At the base of the skull are, however, two bones, 

 the basi- and alisphenoid, that have not been 

 described and that show as well in this as in any 

 other view. The hasisphenoid (just below v and 

 hidden b}^ the pterygoid) was mentioned in connec- 

 tion with the quadrate, with whose posterior mar- 

 gin it articulates. It is an unpaired bone of very 

 irregular shape. Anteriorly it is flattened out to 

 form the rostrum, a rectangular process that forms 

 the posterior part of the interorbital septum; in 

 fact it is the only part of the septum present in 

 a prepared skull, since the rest is cartilaginous. 

 Dorso-laterally the basisphenoid articulates with 

 the alisphenoid ; posteriorly with the basioccipital ; 

 ventrally with the pterygoid; and posteriorly with 

 the exoccipital and basioccipital. On the dorsal 



