$06 MANUAL OF ZOOLOGY SECT, xn 



auricular appendix. Into its cavity on its dorsal aspect 

 open together the right and left pulmonary veins. A large 

 left auriculo-ventricular opening leads from the cavity of the 

 left auricle into that of the left ventricle : this is guarded by 

 a mitral valve, consisting of two membranous lobes or cusps 

 with chordae tendineae and musculi papillares. The columnae 

 carneae are rather more strongly developed in the left ven- 

 tricle than in the right. At the basal (anterior) end of the 

 former is the opening of the aorta, guarded by three semi- 

 lunar valves similar to those at the entrance of the pul- 

 monary artery. The coronary arteries, which supply the 

 muscular substance of the heart, are given off from the 

 aorta just beyond the semilunar valves. The corresponding 

 vein opens into the terminal part of the left precaval. The 

 pulmonary artery divides into two, a right and a left, each 

 going to the corresponding lung. 



The aorta gives origin to a system of arterial trunks by 

 which the arterial blood is conveyed throughout the body. 

 It first runs forwards from the base of the left ventricle, 

 then bends round the left bronchus, forming the arch of the 

 aorta, to run backwards through the thorax and abdomen, 

 in close contact with the spinal column, as the dorsal 

 aorta (Fig. 285, d. ao.\ 



The system of caval veins has already been referred to. 

 From the liver the blood is carried to the postcaval by the 

 hepatic veins. 



The hepatic portal system consists, as in other Vertebrates, 

 of a series of veins conveying blood from the various parts 

 of the alimentary canal to the liver, the trunks of the system 

 uniting to form the single large portal vein (Fig. 283, /. #.). 

 There is no renal portal system. 



The larynx (Fig. 282, lar.} is a chamber with walls 

 supported by cartilage, lying below and somewhat behind 



