XIII 



PHYLUM CHORDATA 



253 



V 



rh 



the last (fourth) epibranchial artery arises the pulmonary artery 

 (I. pul. art. and r. pul. art.), carrying blood to the lung. 



There are two ductus Cuvieri or precawals (d. c.), as in the Dog- 

 fish (p. 156). The right is formed by the union of jugular 

 (I. jug. v. and r. jug. v.\ IracMal (I. br. v. and r. br. v.), and 

 subscapular veins (l.se. 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 postcaval 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 for- 

 wards 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 Elasmobranchs ; it opens 

 into the sinus venosus. The other branch 

 is the renal portal vein ; after receiving 

 tributaries from the posterior region of 

 the body ifc passes to the corresponding 

 kidney. 1 



Brain. The whole brain (Fig. 910) 

 is enclosed in a tough and thick mem- 

 brane, 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 chor&id 

 plexus, passes downwards into the diacoele 

 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 



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

 be best understood at a later stage. 



Fir,. 010. Brain of Ceratodus 

 forsteri, dorsal view. nvd. 

 auditory nerve ; clil. cerebellum ; 

 fiic. facial nerve ; yl. glosso- 

 pharyngeal ; me<L medulla ob- 

 longata ; men. mesencephalon ; 

 oc. oculo-motor nerve ; opt. optic 

 nerve ; pros, prosencephalon ; 

 rh. rhinencephalon (olfactory 

 lobe with olfactory tract and 

 bulb) ; rg. vagus nerve. (Chiefly 

 after Sanders.) 



