4i8 FISHES. 



From the ear-capsule towards 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 Ihe 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 shoulder girdle is a broad cartilaginous bar of 

 double origin. It is fixed dorsally to the vertebral plate. 

 Its dorsal region is distinguished as scapular, its ventral as 

 coracoid. Its 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 fin-rays. 



The hip-girdle is a smaller ventral bar, with 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 fin-rays 

 proceed. The claspers of the males are closely connected 

 with the hind limb, and have a very complex cartilaginous 

 skeleton and an associated gland. 



Nervous System. — The brain (see p. 378-81) has the 

 following parts : — 



(i) 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 pituitary 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. 



(5) The medulla oblongata, with thin vascular roof, 



with dorso-lateral extensions called "restiform 

 bodies." 



