246 



ZOOLOGY 



SECT. 



fish (p. 152). The right is formed by the union of jugular (I. jug. v. 

 and r. jug. v.), brachial (I. br. v. and r. br. v.), and subscapular veins 

 (l.sc. v. and r. sc. v.). The left receives in addition a left cardinal 

 vein (I. post. card.). A. large lateral cutaneous vein, running 

 superficially along the side of the body, opens into the subscapular. 

 A large poslcaval vein (i. v. c.) brings back the greater portion of 

 the blood from the posterior parts of the body ; it is situated 

 somewhat to the right of the middle line, and opens into the sinus 

 venosus between the two hepatic veins. A postcaval occurs in the 

 Dipnoi alone amongst Fishes, but is universal in all the higher 

 classes. Posteriorly the cardinal and the postcaval are formed by 

 the bifurcation of a median caudal vein ; close to its origin each 

 receives the efferent renal veins bringing back the blood from the 

 kidney. The blood from the pelvic fin is brought back by an iliac 



vein which divides into two branches 

 pelvic and renal portal. The former, 

 running forwards and inwards, unites 

 mesially with the corresponding vessel 

 of the opposite side to form a median 

 abdominal vein a vessel universal in the 

 Amphibia, and perhaps corresponding to 

 the lateral veins of the Elasrnobranchs ; 

 it opens into the sinus venosus. The 

 other branch the renal portal vein- 

 after receiving tributaries from the pos- 

 terior region of the body passes to the 

 corresponding kidney. 1 



Brain. The whole brain (Fig. 921) is 

 enclosed in a tough and thick membrane, 

 which becomes glandular in two positions 

 on the roof of the diaccele, and on 

 that of the metacoele. In the former 

 position this glandular development of 

 the enclosing membrane, or choroid 

 plexus, passes downwards into the dia- 

 ccele and is developed into a spongy 

 mass which is prolonged forwards to 

 the anterior end of the prosencephalon. 

 The prosencephalon (pros.) presents 

 two elongated hemispheres, which are 

 completely separated except posteriorly, 

 where they are united by a narrow 

 The contained cavity is divided into two by the 

 prolongation of the choroid plexus already referred to. The 

 nervous wall of the hemisphere (pallium) is very thin and is 



1 How far this arrangement combines Fish-like and Amphibian characters 

 will be best understood at a later stage. 



- ainl 



Tried 



FIG. 921. Brain of Ceratodus 

 lorsteri, dorsal view. aud. 

 auditory nerve ; ell. cerebellum ; 

 dia. diencephalon ; fac. facial 

 nerve ; gl. glossopharyngeal ; 

 med. medulla oblongata ; meso. 

 mesencephalon ; oc. oculomotor 

 nerve ; opt. optic nerve ; pros. 

 prosencephalon ; rh. rhinen- 

 cephalou (olfactory lobe with 

 olfactory tract and bulb) ; vg. 

 vagus nerve. (Chiefly after 

 Sanders.) 



commissure. 



