306 ZOOLOGY SECT. 



that enter the neural canal and others that supply the muscles 

 and integument. 



The venous blood from the tail is brought back by means 

 of a caudal vein (Fig. 913, c.). This bifurcates at the base of the 

 tail to form the two pelvic (lateral) veins (pi.) ; these unite to form 

 the median epigastric or abdominal (ep. g.), which eventually enters 

 the left lobe of the liver. Entering the pelvic veins are the 

 femoral and sciatic veins from the hind limb. Arising from the 

 pelvic are the renal portal veins distributed to the substance of 

 the kidneys. The efferent renal veins, carrying the blood from 

 the kidneys, combine to form a pair of large trunks, which soon 

 unite to form the median post-caved. The post-caval runs forwards 

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

 the liver, enters the sinus venosus. 



Two precavals, 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 subclavian. On the left side the precaval is formed by the 

 union of internal jugular and subclavian, the left external jugular 

 being absent. 



The liver is supplied, as in 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. 913, c. ad.) are two masses of fat of 

 somewhat semi-lunar 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. 913 and 914, 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. 913, 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. 915 and 916) presents all the parts that 

 have been described in the brain of the Frog (p. 263) with some 

 minor modifications. The two cerebral hemispheres (parencephala) 



