328 ZOOLOGY sect. 



towards the heart, and, after receiving the wide hepatic vein from 

 the liver, enters the sinus venosus. 



Two preeavals, right and left, carry the blood from the anterior 

 extremities and the head to the sinus venosus. The right precaval 

 is formed by the union of the internal and external jugular and 

 the mbclavian. On the left side the precaval is formed by the 

 union of ijiternal jugular and stibclavian, the left external jugular 

 being absent. 



The liver is supplied, as is other Vertebrates, by a hepatic portal 

 system of vessels, blood being carried to it by a portal vein, 

 formed by the union of gastric, pancreatic, splenic, and mesenteric 

 veins. 



The adipose bodies (Fig. 968, c. ad.) are two masses of fat of 

 somewhat semilunar shape in the posterior part of the abdominal 

 cavity, between the peritoneum and the muscles of the body-wall. 



The thyroid is a whitish, transversely-elongated body on the 

 ventral wall of the trachea, a short distance in front of the heart. 



The spleen (Figs. 968 and 969, spl.) is a small red body lying 

 in the mesogaster, near the posterior end of the stomach. 



Organs of Respiration. — A slit-like aperture, the glottis, 

 situated behind the tongue, leads into a short chamber, the larynx, 

 the wall of which is supported by cricoid and arytenoid cartilages. 

 From the larynx an elongated cylindrical tube, the trachea, passes 

 backwards on the ventral side of the neck. Its wall is supported 

 by a, large number of small rings of cartilage, the tracheal rings. 

 Posteriorly the trachea bifurcates to form two similar but narrower 

 tubes, the bronchi, one entering each lung. The lung (Fig. 968, Ig) 

 is a fusiform sac, the inner lining of which is raised up into a net- 

 work of delicate ridges, having the appearance of a honeycomb ; 

 these ridges are much closer and more numerous towards the 

 anterior than towards the posterior end of the lung. 



The brain (Figs. 970 and 971) presents all the parts that 

 have been described in the brain of the Frog (p 284), with some 

 minor modifications. The two cerebral hemispheres (parencephala) 

 (Fig. 970, c.h.) are oval bodies, somewhat narrower in front than 

 behind, closely ajDplied together. Each is prolonged anteriorly 

 into the corresponding olfactory peduncle or tract, somewhat dilated 

 in front to form the olfactory bulb (olf.) from which the olfactory 

 nerve arises. In the interior of each is a cavity, the lateral 

 ventricle or paraccele, sending a. prolongation forwards into the ol- 

 factory bulb, and communicating behind by a small aperture, the 

 foramen of Monro (D,/. m.), with the diacoele (v.S). Through the 

 foramen of Monro there passes into each paraccele a vascular 

 process of pia mater, the choroid plexus (ch. p.) : immediately above 

 and behind this is a hippocampcd commissure {c.p.a) connect- 

 ing together two areas known as hippocampji, one on the mesial 

 surface of each hemisphere. On the floor of each paraccele is a 



