THE MORMTRID^, NOTOPTERIDJi:, AWD HTODONTIDiE. 203 



inflated, the bulla being formed by the pro-otic and basioccipital 

 at the side, and by the posterior end. of the parasphenoid. below. 

 Behind the bony swelling is a ventro-lateral vacuity bounded 

 above by the opisthotic and. pro-otic, and internally by the 

 basioccipital. This vacuity lodges the inner and upper portion 

 of a rather large air-vesicle, the outer and lower walls of which 

 are fibrous, and are consequently wanting in a macerated skull. 

 The anatomy of this diverticulum of the swim-bladder has been 

 minutely described by Bridge (I. c), who terms it the " auditory 

 csecum." 



The basisphenoid is of fair size. It is nearly horizontally 

 disposed, has no descending limb, and is slightly convex on its 

 lower surface. At its sides it touches both alisphenoid and 

 pro-otic. The foramen between the alisphenoid and the pro- 

 otic is situated unusually high up the back of the orbit. The 

 two alisphenoids meet one another behind the orbitosphenoid, 

 which is rather exceptional ; and the olfactory lobes run the 

 whole of their course within the orbitosphenoid and prefrontal 

 bones. 



The parasphenoid is broadened out into a rhombus in its 

 hinder portion, and its posterior extremity lies beneath the 

 middle of the length of the basioccipital, or even a little in 

 advance of this. The eye-muscle canal is short and blind. The 

 parasphenoid bears an elongated patch of teeth, and its lateral 

 wings extend a fair distance up the front of the pro-otic bones. 

 The vomer bears a small patch of teeth near its anterior 

 end. It extends rather more anteriorly than the mesethmoid, 

 which fits closely on the front of the prefrontals, the ethmoid 

 region of the cranium being short. There is an extensive union 

 of the right and left prefrontals in the median plane of the 

 head. 



Temporal and Freopercular Series (fig. 12). — The post- 

 temporal has the form of a tube, elliptical in section, and 

 opening obliquely at both ends on its cutaneous aspect. The 

 anterior end is attached by fibrous tissue to the back of the 

 exoccipital and to the upper part of the opisthotic. The lower 

 edge of this bone must thus be regarded as the opisthotic limb. 

 The epiotic limb is wanting. In Notopterus afer (Brit. Mus. 

 95.7.18.49, Old Calabar) there is a separate opisthotic limb, 

 a long, slender, delicate rod. 



The supratemporal is an elliptical scale of bone, which does 

 not carry the sensory tube, but lies at a slightly higher level. 



