52 



MANUAL OF ELEMENTARY ZOOLOGY 



tr.a. _ 



concerned in the preparation of nitrogenous waste matters 

 for excretion. Its removal is not fatal. 



The fat bodies are two orange-coloured tufts of flattened 

 processes, attached in front of the ovary or testis to the 

 dorsal wall of the body cavity. They consist of fatty tissue 

 (see p. 97) which, like the reserves in the liver, increases 

 during the summer and decreases during the winter sleep, 

 when it is being drawn upon for nourishment, particularly in 



the preparation of germ 

 cells for breeding in the 

 spring. 



The heart of the frog 



is a hollow, 



Vascular r n n i r a 1 



System : Heart. 1 - UIHL,U ' 



muscular 



organ, which lies with 

 the apex backwards in 

 the body cavity, be- 

 tween the breast-bone 

 and the gullet. It is 

 enclosed in a thin sac, 

 the pericardium, whose 

 cavity is a part of the 

 body cavity separated 

 from the rest during 

 development, the heart 

 having the same rela- 

 tion to it that the ali- 

 mentary canal has to 

 the pleuroperitoneal or 

 general body cavity — 

 that is, being covered 

 by a continuation of 

 the pericardial membrane as the gut is by the peritoneum. 

 Five chambers may be recognised in the .heart. Of these 

 the most conspicuous is the ventricle, a large, conical struc- 

 ture, with thick, muscular walls, from which arises in front, 

 on the right side of the ventral surface, the much smaller, 

 tubular truncus arteriosus. The right and left auricles or 

 atria are relatively thin-walled chambers, the right larger 

 than the left, separated by a septum and lying in front of 



FlG. 26. — The heart of a frog, seen from 

 the ventral side. 



c.a., Carotid arch; car., carotid artery; c.gl., 

 carotid gland ; /.a., lingual artery; pc.a., 

 pulmocutaneous arch; put., penrardium ; 

 r.au., Lai, , right and left auricles; s.v.c, 

 superior vena cava ; sy.a., systemic arch ; 

 tr.a., truncus arteriosus ; v., ventricle. 



