VERTEBRAL COLUMN. 



37 



each centrum (Fig. 26, J., en 1 ), which articulates with a convexity (en) on the 

 next vertebra behind (opisthocoelous vertebra). The notochord (except in 

 the caudal region) entirely disappears in the adult ; in the larva it is seen to 

 be expanded vertebrally, and constricted intervertebrally, a condition of 

 things which appears again in the higher types, as, for instance, in Reptiles. In 

 a still earlier larval stage, however, the constrictions are vertebral, as in other 

 Fishes (see Fig. 27). 



The primitive character of the vertebral column of Fishes is 

 shown by the fact that the arches only meet dorsally in rare in- 

 stances. As a rule, the closing in of the arch is effected by special 



FIG. 26. PORTION OF THE VERTEBRAL COLUMN OF Lepidosteus. 

 (After Balfour and Parker.) 



A, a vertebra from anterior surface ; B, two vertebrae from the side ; en, anterior 

 convex face, and cn l , (posterior concave face of centrum ; h. a, basal process ; 

 n. a, upper arch; i.c, intercalary cartilages; ZJ, longitudinal ligament; i.s, 

 interspinous bone. 



pieces of cartilage and by an elastic longitudinal band (Figs. 22, 

 26, i.c, LI) which is always present. This description of the upper 

 arches applies also to the lower ones present in the caudal region. 

 Elasmobranchs and Ganoids possess a greater number of vertebrae 1 

 than Teleosteans, in which we seldom meet with more than 70 : 

 the Eel, however, possesses more than 200. In Rays and ChimseraB 

 only amongst Fishes are definite articulations formed between the 

 skull and vertebral column. 



1 In Alopecias vulpes there are 365 ; in Carcharias glaucus, 240 ; in 

 Lamna, 150; in Pristiurus, 140; in Scyllium, about 124; inSquatina, 117. 



