AMPHIBIA. 



201 



verse processes of vertebrae 3 and 4, and are connected with the 

 subscapular veins. The posterior lymph-hearts (Fig. 56) are 

 placed one on each side of the urostyle, not far from its posterior 

 end, in a triangular space between the muscles. Each com- 

 municates with a small vein which opens into the cross-branch 

 between the sciatic and femoral veins of its side. 



Fig. 57. Fig. 58. 



Fig. 57. MUSCLE-FIBRES FROM HEART OF FROG (from Landois and 

 Stirling), much enlarged. 



Fig. 58. SMALL ARTKRY SHOWING THE COATS (from Landois and 

 Stir lint/). a, Endothelium ; b, elastic membrane; c, muscular coat; 

 d, connective-tissue coat. 



Closely connected with the circulatory system are several small 

 organs known as ductless glands. These are the spleen and the 

 thymus and thyroid " glands." The spleen is a small rounded body, 

 of dark red colour, lying in the mesentery, near the commence- 

 ment of the large intestine. The thymns glands are two small 



