87 



portion of the bone ; and indicating, like the corresponding membranous niumrr in 

 tin- Crtlrartim, tin- primitive platv of the cranial end of the uotochord. The expanded side*, 

 originally mAt* of the cart iUginoun portion, bend down to abut against tin- basrs of thr ptr- 

 rygoid plate*. In this expansion of the baaiaphenoid the J^fntlotiren retemblea the I'layit,- 

 tomn, and alto the Batrarhian Iteptilcs. 



Two ridge* rue from the upper surface of the occipito-sphenoidal plate, m-nr its outer 

 fin, and rapport die cartilaginous lateral wall* of the cranium. The cranial cavity is 

 defended above by a longitudinal bony roof, nearly co-extensive with the bony floor bcnralh . 

 the roof commences behind by the spine or point which overhangs the exoccipitals, gradual!) 

 expands as it advances, resting upon the cartilaginous wall* of the cranium, is tben suddenly 

 contracted, and is united anteriorly by fibrous ligament to the ascending process of thr 

 palato-maxillary arch, and to the base of the nasal plate. A strong sharp crest or spine rise* 

 from above the whole of the middle line of the cranial roof-bone, which may be regarded a* 

 representing the mid-frontal, the parietal, and superoccipital bones, or, in more general term*, 

 the neural spines of the three cranial vertebra* ; but this supra-cranial bone not only covers 

 the medulla oblongata, cerebellum, optic lobes, pineal sac and cerebral hemispheres, but also 

 the olfactory lobrs. 



The lateral cartilaginous walls of the cranium are continued forwards from the acoustic 

 capsule between the basal and superior osseous plates : the part perforated by the fifth pair 

 of nerves and protecting the side of the optic lobes, represents the great ala of the sphenoid : 

 the next portion in advance, protecting the sides of the cerebral hemispheres and perforated 

 by the optic nerve, answer* to the orbital ala of the anterior Kphcnoid : and the cartilage ter- 

 minate! by a part which is perforated by the olfactory nerve, and which abuts laterally against 

 the ascending or palatine process of the maxillary arch. 



The outward extension of the lateral cartilages of the cranium downwards, in the form of 

 a broad triangular plate, the apex of which forms the articulation for the lower jaw, is like 

 that which we see in the Chimara ; but ossification has extended along two tracts, which 

 converge as they descend, one from behind to the outer, the other from before to the inner 

 side of the cartilaginous maxillary joint, which these bony plate* strengthen and support like 

 the backs of a bonk. The posterior of these bony arches is obviously the homolnguc of the 

 tympanic pedicle in the Sonatina : the anterior bony arch as plainly answers to the pterygoid 

 buttress in Osseous Fishes ; bat it is here confluent with the coalesced palatine and superior 

 maxillary bones, the dcntigerous part of which extends outwards, downwards, and backward*, 

 but does not reach, as in the Sharks and Kays, the mandibular joint. 



From the upper part of the palato-maxillary portion a compressed sharp process ascend* 

 obliquely backwards, and terminates in a point ; the inner side of this process is closely- 

 attached by ligament to the fore and outer part of the frontal portion of the epicranial bone . 

 the outer aide of the process is excavated for the reception of the outer and anterior process 

 of the postfrootal bone. This bone, in connection with the ascending process of the maxil- 

 lary, forms the upper part of the orbit, and behind this connection it sends out the post- 

 orbital process, beyond which it extends backwards, freely overhanging the fronto-occipital. 

 and gradually decreasing to a point, which terminates just above the occipital spine, in thr 

 position of the mastoid, in bony Fishes, and giving attachment to the anterior end of the 



