262 
(a) 
(b) 
ANATOMY OF THE RABBIT. 
The bicuspid or left atrioventricular valve (valvula bicus- 
pidalis) is similar in general structure to the tricuspid valve 
of the right ventricle, but is more nearly circular in form, 
with stout, closely grouped papillary muscles. 
The semilunar valves of the aorta are three in number, and 
are similar to those of the pulmonary artery. 
4. Examination of the lungs and their connections (Figs. 44, 
83). 
The removal of the ventral wall of the thorax opens the pleural 
cavities by taking away a considerable portion of the costal pleura, 
which is adherent to the internal surfaces of the ribs. The chief 
features may be made out as follows: 

(a) Each pleural cavity (cavum 
pleurae) is a closed serous sac, 
the lining membrane, or 
pleura, being distributed over 
the costal surface as the costal 
pleura, partly over the ante- 
rior surface of the diaphragm 
Fic. 83. Plan of the respiratory as the diaphragmatic pleura, 
tubes as seen from the ventral surface. . 
tr, trachea; br, br’, left and right and Over the surface of the lung 
bronchi; ep, eparterial bronchus; s,m, 
m’, i, i’, bronchial rami to superior, as the pulmonary pleura. 
middle and inferior lobes; ll, Im, E 
bronchial rami to lateral and medial Posteriorly the pulmonary 
obules. 
(b) 
(c) 
pleura passes from the medial 
margin of the left lung to the medial lobule of the right and 
thence backward to the diaphragm, forming a broad sheet of 
attachment, the pulmonary ligament (lig. pulmonale). 
The lungs (pulmones) are paired expansible structures, the 
surfaces of which are free, except posteriorly, where they 
are attached to the diaphragm through the pulmonary liga- 
ment, and medially where they are connected with the 
pulmonary bloodvessels and the respiratory tubes. 
Each lung is divided into three portions, the superior, 
middle, and inferior lobes. On account of the smaller 
size of the left lung, the superior lobe is imperfectly develop- 
ed. On the right side the inferior lobe is divided into two 
portions, the medial and lateral lobules, the inferior caval 
vein passing between them. 
