50 



MORPHOLOGICAL TYPES 



formed. Rising up from the centra are the neural arches, 

 which enclose the spinal cord in a canal. Alternating with 

 these are interdorsal cartilages. The ventral nerves emerge 

 behind the neural arches, and the dorsal roots behind the 



Fig. 26. — Scyllium : ventral view of, A, pectoral, and B, pelvic girdle. 



b y basipterygium ; c, coracoid region ; d, skeleton of clasper (present in 

 the male) ; ms, mesopterygium ; mt , metapterygium ; n, nerve foramen ; 

 p> pelvic cartilage ; pr, propterygium ; r, radials ; s, scapular region. 



interdorsal cartilages. Ventral extensions of the basiventrals 

 beneath the centra in the tail-region form haemal arches, in 

 which blood-vessels run. Lateral extensions of the basi- 

 ventrals give rise to the ribs. They extend in the septum 



