THE SKELETON. 537 



cartilage attached dorsally to the crest of the vertebral plate. 

 The ventral region is distinguished as the coracoid, and is 

 separated from the dorsal or scapular region by three facets, 

 to which the three basal pieces of the pectoral fin are fixed. 

 A separated portion of the girdle forms the supra-scapula, 

 which connects the scapula with the crest of the vertebral 

 plate. / 



Of the three basal pieces of the fin, the anterior or 

 propterygium and the posterior or metapterygium are 

 large, the median or mesopterygium is small. All bear 

 jointed radials, which are parts of the endoskeleton ; a 

 few radials articulate directly with the shoulder-girdle (see 

 Fig. 282). The true fin-rays, comparable to the dermal 

 rays in the fins of Bony Fishes, are represented by " horny " 

 (or, more strictly, elastoidin) fibres. These are intercellular 

 products of mesoderm (mesenchyme) cells. 



The pelvic girdle is simpler than the pectoral, and is not 

 fixed to the vertebral column. Its dorsal region is pro- 

 longed into an iliac process, while anteriorly a prepubic 

 process projects from the ventral (pubic) bar. The girdle 

 bears two articulating facets, to the posterior of which the 

 strong basal piece or metapterygium of the hind-limb is 

 attached. From this, and from the anterior facet of the 

 girdle, the jointed radials proceed. The claspers of the 

 males are closely connected with the posterior part of the 

 hind-limb, and have a complex cartilaginous skeleton and 

 an associated gland. 



The brain. The brain (see p. 483) has the following 

 parts : 



I. The fused cerebral hemispheres or prosencephalon, with a 

 nervous roof, and without ventricles. 



cartilage (M.} forming the lower jaw; and the hj^o-mandibular 

 (h.m.') which suspends the jaws to the skull. A little farther 

 back are seen the five branchial arches and the anterior hyoid 

 arch ; h.br., the fifth hypobranchial ; v.pl., the vertebral plate. 

 At the right is seen the skeleton of the paired fins, at the l^ft 

 the surface of the skin with the sensory tubes (s.t.)', sc., the 

 scapular region of the shoulder-girdle, with the scapular 

 fontanelle ; c., the coracoid region; p.pt. t the anterior basal 

 cartilage or pro-pterygium ; m.pt., the meso-pterygium ; int.pt., 

 the meta-pterygium all three bear jointed radials, while a few, 

 as shown here, articulate directly with the shoulder-girdle ; 

 pu., pubic bar of pelvic girdle ; st., stomach ; s.v., spiral valve 

 of intestine. 



