482 FISHES. 



From the ear capsule to the articulation of upper and 

 lower jaw there extends on each side a club shaped cartilage 

 known as the hyo-mandibular. Attached to this is a slender 

 three jointed rod the hyoid. 



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 

 nose capsule, an antorbital cartilage uniting the nose capsule 

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

 supporting the rudimentary gill in the spiracle. 



The dorsal or scapular region of the pectoral girdle is 

 fixed on each side to the crest of the vertebral plate by 

 means of a supra-scapula. The ventral region of the girdle 

 is distinguished as the coracoid portion. The outer edge 

 bears three facets, to which the three basal pieces of the 

 pectoral fin are fixed. 



Of these three basal pieces the anterior or propterygium 

 and the posterior or metapterygium are large, the median or 

 mesopterygium is small. All bear jointed radials. 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 pre-pubic 

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

 bears two articulating facets, to the posterior of which the 

 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 hind limb, and have a 

 very complex cartilaginous skeleton and an associated gland. 



The Brain. 



The brain (see p. 435) has the following parts : 



(1) The fused cerebral hemispheres or prosencephalon, with a 



nervous roof, and without ventricles. 



(2) The thalamencephalon or region of the optic thalami, with 



a thread-like pineal body above, infundibulum and pituit- 

 ary body below, thinly roofed third ventricle within. 



(3) The mesencephalon or mid-brain with the optic lobes above, 



the crura cerebri below, the iter passing between. 

 (4) The cerebellum with an anterior and a posterior lobe, both 

 marked by ridges and grooves. 



