THE SKELETON. 515 



hyo-mandibular or suspensorium. It is the upper half of 

 the second arch. Attached to it is a slender four-jointed 

 rod the lower half of the hyoid arch. 



Then follow five branchial arches, each primarily four- 

 jointed, forming the framework of the gill-bearing region. 



Of less importance are four labial cartilages about each 

 nasal capsule, an antorbital cartilage uniting the nasal 

 capsule with the end of the pectoral fin, and a spiracular 

 or meta-pterygoid cartilage supporting the rudimentary gill 

 in the spiracle. 



The pectoral girdle forms an almost complete hoop of 

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

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

 fibres. 



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. 466) has the following 

 parts : 



i. The fused cerebral hemispheres or prosencephalon, with a 

 nervous roof, and without ventricles. 



