94 STUDIES ON THE ELASMOBRANCH SKELETON, 



same transverse plane as the point of junction of the anterior 

 and posterior semi-circular canals, and therefore excavated in the 

 side of the cranium proper and not on the postero-lateral process. 

 The opening of the facial is directly in front of this articular 

 cavity, and is separated by a broad ridge from that of the 

 trigeminal. The supra-orbital ridge is very prominent and forms 

 to some extent a roof to the inner part of the orbit ; it ends 

 behind and in front in prominent post- and prae-orbital processes. 

 There is a very broad and thin lamellar basal plate, nearly 

 horizontal in position, but inclined slightly downwards externally ; 

 it presents a rather small oval opening in its hinder portion close 

 to the lateral wall of the cranium. 



The palato-basal articulation takes place through the interme- 

 diation of a very thick and short ligament inserted immediately 

 in front of the orbit, where there is a small but well-marked 

 articular surface looking outwards and forwards. 



The ethmoidal canal is not even represented by a notch.* The 

 prefrontal opening is large and its lateral borders diverge anteriorly 

 unlike those of Scyllium. In front of it the basis cranii rises up 

 and is extended into three thin lamellar processes, of which the 

 middle one or rostrum is nearly straight and ends in a free 

 extremity between the nasal capsules, while the lateral become 

 rather expanded, and, their anterior ends curving downwards, 

 form a part of the roof of the corresponding nasal capsule. 

 Immediately behind the frontal foramen is a slender process which 

 passing outwards and forwards, becomes greatly expanded at its 

 extremity to form the outer and inferior wall of the nasal capsule. 



The labial cartilages form a chain of three strong bones on either 

 side, forming a nearly complete ring round the mouth only inter- 

 rupted by a space in the middle above and below. 



The proximal extremity of thehyomandibular presents anteriorly 

 a stout peg-like process corresponding to the deep articular cavity of 

 the side of the skull. Distally it presents a broad surface for the 



* This is a marked point of distinction between the present form and Scyllium and 



Clu i lose y Ilium. 



