34 ZOOTOMY. 



several contiguous neural spines. Connected with the 

 distal ends of the radial cartilages are numerous horny fila- 

 ments, the dermal fin rays, which support the distal 

 portion of the fins. 



16. The skeleton of the caudal .fin is rudimentary, con- 

 sisting of a few very small radial cartilages attached to the 

 posterior caudal vertebrae : the fin is supported almost 

 entirely by dermal fin rays. 



VI. In the brain-case, note 



17. The flat floor (basis cranii, Fig. 10) and roof 

 (tegmen cranii). 



Fig. 14. — Raja nasuta. A caudal vertebra, seen from the front 

 (nat. size). 



c, centrum, /;./, haemal process : h.s, hsemal spine : «./, neural 

 process : ii.s, neural spine. 



18. The foramen magnum, a large rounded aperture 

 on its posterior wall, placing the cranial cavity in communi- 

 cation with the neural canal of the vertebral column. The 

 cartilage surrounding the foramen magnum constitutes the 

 occipital region of the skull. 



19. The occipital condyles, rounded protuberances, 

 one on either side of the foramen magnum, for articulation 

 with the corresponding surfaces on the anterior vertebral 

 plate : between them the base of the skull is scooped out 

 for the reception of the odontoid process. 



20. The auditory capsules (Fig. 10, au), large out- 

 standing masses of cartilage, one on either side of the 



