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 
jarge, 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” 
(ox, 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 (JZ.) forming the lower jaw; and the hyo-mandibular 
(4.m.) which suspends the jaws to the skull. A little farther 
back are seen the five branchial arches and the anterior hyoid 
arch ; 4.47., the fifth hypobranchial ; v.f/., the vertebral plate. 
At the right is seen the skeleton of the paired ‘fins, at the left 
the surface of the skin with the sensory tubes (s.4.); sc., the 
scapular region of the shoulder-girdle, with the scapular 
fontanelle ; c., the coracoid region; 2.f2., the ‘anterior basal 
cartilage or pro-pterygium ; 7./., the meso-pterygium ; 77.f4., 
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 ; s¢., stomach; s.v., spiral valve 
of intestine. 
