VERTEBRAL COLUMN* 



439 



modified at metamorphosis : the hyoid cartilage of the 

 adult (p. 44) represents the hyoid and first branchial arch. 

 In addition to the parts of the dogfish's skull described 

 above there are certain small cartilages of minor importance 

 in relation with the nostrils, spiracle, mouth, and outer 

 sides of the branchial arches (e.g., Ib and ex. br in Fig. 112). 



The vertebral column has the general character of a 

 jointed tube surrounding the spinal portion of the neural 



fcrf fr 'i.n.p npn. 



7l.S.p 



nlc 



n.a 



n.sp 



h.a 



FIG. 113. Vertebrae of Scyllium canicula. (X 2.) 

 A and B from the trunk, C and D from the middle of the tail ; A and C, two vertebras 



in longitudinal section ; B and D, single vertebra viewed from one end. 

 b. calcined portion of centrum : c. centrum ; for. foramen for dorsal, and for', for 

 ventral root of spinal nerve ; A. a. haemal arch ; h. c. hasmal canal ; h. sp. haemal 

 spine ; i. n. p. interneural plate ; n. a. neural arch ; n. c. neural canal ; n. />. 

 neural process and plate ; n. sp. neural spine ; ntc. intervertebral substance 

 (remains of notochord) ; tr. pr. transverse process r. proximal portion of rib. 



canal. Lying beneath this cavity, i.e., between it and 

 the coelome, is a longitudinal row of biconcave or 

 amphiccelous discs, the vertebral centra (Fig. 113.. c ; 

 Fig. 117, en) : they are formed of cartilage, but have 

 their anterior and posterior faces densely calcined ; 



