SANGUIFEROUS SYSTEM. 



491 



common trunk (139. o.) of the two pulmonary arteries 

 (139. p. q.) 



FIG. 139. 

 .ft 



Two strong semilunar valves check the return of the 

 venous blood from the right auricle into the sinus venosus, 

 but the same protection is not observed at the single very 

 oblique orifice, by which the two pulmonary veins enter the 

 left auricle. The ventricle is of great size, much extended 

 transversely, depressed in form, with a rounded obtuse apex, 

 with very thick muscular parietes, especially in its left por- 

 tion, and the innumerable free fleshy columns reduce its in- 

 terior to a loose reticulate spongy texture. Its exterior 

 surface is generally connected with the pericardium by 

 several tendinous filaments, and the same are sometimes 

 observed passing from the ventricle to the exterior of the 

 auricles. The septum ventriculorum is developed to a va- 

 riable degree in the species of this order, being least percep- 

 tible in the land tortoises, and most distinct in the marine 

 turtles, but is less developed than in the saurian reptiles. 



