146 ZOOLOGY. 



innominate. The subclaviaii brings blood not only from 

 the arm (brackial vein), but also from the skin and certain 

 muscles by a large musculo-cutaneous vein. The azygos of 

 the rabbit is not found in the frog. 



The postcaval, as in the rabbit, receives paired hepatic, 

 paired genital, and paired renal veins, but that is all : no 

 blood from the hind lirnbs or hind part of the body passes" 

 directly into the postcaval. The explanation of this is that 

 the frog has two portal systems an hepatic-portal, re- 

 sembling in all essentials that of the rabbit, and a paired 

 renal-portal in which the kidneys play the part takeiTby 

 the liver in the former. Blood from each hind -limb is con- 

 veyed by two main veins femoral and sciatic. The former 

 divides into pelvic and femoro-renal. The right and left 

 pelvics unite into a median abdominal vein,* which flows 

 along the ventral body-wall and into the hepatic-portal 

 system. The femoro-renal unites with the sciatic of its 

 own side into a renal-portal, which, after further receiving 

 a dorso-lumbar from the body- wall, branches out into the 

 kidneys. It is interesting to note that the blood from the 

 renal arteries goes direct to the glomeruli, while that from 

 the renal-portal vein goes to the capillary-plexus around 

 the kidney-tubules. 



// Thus the whole of the blood from the hind limbs and 

 I adjacent regions must pass through a second set of capillaries 

 (either those of the liver or those of one of the kidneys) 

 before reaching the heart. 



9. The Lymphatic System. The frog has a lymphatic 

 system like the rabbit's, but its largest vessels take the form 

 of large, ill-defined spaces rather than true vessels. Such 

 spaces are known as sinuses. There is a large sub-vertebral 

 lymph-sinus between the dorsal part of the peritoneum and 

 the vertebral column, that is, just in the position of the 

 thoracic duct, from which it differs in the absence of well- 

 defined walls : into it the chyle is poured by the lacteals. 

 There are sub-cutaneoiis lymph-sinuses which cause the great 



* Commonly called the anterior abdominal. " Anterior " here is 

 used in the human-anatomy sense of "ventral," and is therefore 

 misleading. 



