GREGORY: FISH SKULLS 



169 



teeth to near the posterior end of the maxilla, the normal appearance of the circumorbital 

 plates, the presence of an orbitosphenoid and the retention of a symplectic, exist side by- 

 side with specializations and losses, such as the close connection of the quadrate with the 



epiot 



Notopteras sp 



Fig. 61. Notoptfrus sp. 



preopercular by means of two serrated ridges, the incipient reduction of the opercular, 

 which is membranous around the margin, and the loss of the subopercular. 



Above the pterotic is a large "lateral cranial foramen," leading in the dried skull 

 directly into the cranial cavity. This is a marked point of resemblance to the mormyrids, 

 in which this foramen is occupied by a thick-walled vesicle (Ridewood, 1904r, p. 189). 

 "The base of the skull is inflated," writes Ridewood (op. cii., pp. 202, 203), "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 [1900], who terms 

 it the 'auditory caecum.'" Thus the notopterid air-bladder, like that of the mormyrids, 

 clupeids, cyprinids and other malacopterygian groups, gives the impression of having sent 

 out various exploratory diverticula which in the different families succeeded in penetrating 

 the auditory chamber by different routes. 



