THE SKULLS OF FISHES. 197 



to the nasal sacs. The commencement of the narrow neck is 

 perforated on each side by the optic foramina (II.). The hinder 

 dilatation contains the mass of the brain, and, on each side, 

 chambers for the auditory organs, which communicate with it, 

 are situated. The posterior edge of the inter-orbital septum 

 bounds this chamber in front, above the " neck." In front of 

 the anterior boundary of the inter-orbital septum, and above 

 the olfactory division of the skull cavity, there is a curious 

 chamber filled with fatty matter, and open in front and behind, 

 which is traversed by the nasal division of the fifth nerve. 



Miiller well says, " The skull of Chimasra is most like that 

 of a tadpole ; " * but if we interpret the former strictly by the 

 latter, as I believe ought to be done, the results will be some- 

 what different from those at which Miiller arrives. The plate 

 C, D answers precisely to the sub-ocular arch of the lamprey and 

 to the corresponding arch in the tadpole's skull, though it is 

 chondrified throughout, and not perforated by a large a]3erture, 

 as in the two latter animals. But, admitting this, the further 

 development of the frog proves that the sub-ocular arch answers 

 to the common suspensorium of the hyoid and mandible, and to 

 the palatine, pterygoid, and quadrate bones ; and that it has 

 nothing to do with the maxilla or premaxilla. The large 

 posterior upper jaw teeth of the Chimseroids (c), therefore, being 

 attached to the under surface of the anterior part of the sub- 

 ocular plate, must be palatine or palato-pterygoid teeth. The 

 small anterior teeth (a), on the other hand, are fitted into fossae, 

 or alveoli (B), which are situated immediately under the floor of 

 the nasal chambers, in the vomerine region of the skull, and 

 must be regarded as vomerine teeth — as, indeed, Cuvier sug- 

 gested. On the other hand, I think Midler's view that the 

 cartilages (d, e, &c.) are accessory labial cartilages, and not, as 

 Cuvier supposed, representatives of preniaxillae, in axillae, &c, 

 has everything in its favour. 



c. The cartilaginous cranium, with a mandible and with a 

 moveable suspensorium. 



This form of cranium is met with in the sharks and rays, 

 and may be illustrated by an account of that of Squat ina, the 

 * Vergleichende Anatomic tier Myxinoiden. Erster Tlieil, p. 159. 



