362 DISSECTION OF THE rabbit. 



ii. The orifice of the pulmonary artery is at the 

 left anterior angle of the ventricle, and is 

 guarded by three pocket-like semilunar valves, 

 the free edges of which are directed away 

 from the ventricle. 



Note the position of the valves from above ; slit up the 

 pulmonary artery between two of them, and examine them. 



b. The left ventricle. 



Remove the outer wall in the same manner as that of the 

 right ventricle. 



i. The mitral valve, guarding the left auriculo- 

 ventricular aperture, resembles the tricuspid 

 valve, except that there are only two flaps, 

 and the musculi papillares are much larger. 



ii. The orifice of the aorta is at the base of the 

 ventricle, immediately to the right of the 

 mitral valve. It is guarded by three semi- 

 lunar valves, one of which is dorsal, and the 

 other two ventro-lateral in position. Imme- 

 diately beyond the two latter valves the 

 coronary arteries, which supply the heart, 

 arise from the aorta. 



The heart of a sheep may be dissected with advantage, 

 and it differs so little from that of the rabbit, that the fore- 

 going description applies, with very little modification, to it. 

 The chief differences are the union of the two anterior venae 

 cavae before entering the auricle, and the presence of a muscu- 

 lar ' moderator ' band crossing the cavity of the right ventricle 

 obliquely. 



VII. DISSECTION OF THE RENAL AND REPRODUCTIVE 



SYSTEMS. 



In the rabbit, as in the dog-fish, certain parts of the primi- 

 tive kidneys and their ducts lose their excretory function, and 



