262 



Anatomy of the Rabbit. 



(a) 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. 



(b) 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 

 as the diaphragmatic pleura, ' 

 and over the surface of the lung 

 as the pulmonary pleura. 

 Posteriorly the pulmonary 

 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. 



Fig. 83. Plan of the respiratory 

 tubes as seen from the ventral surface, 

 tr, trachea; br, br', left and right 

 bronchi; ep, eparterial bronchus; s.m, 

 m', i, i', bronchial rami to superior, 

 middle and inferior lobes; 11, Im, 

 bronchial rami to lateral and medial 

 lobules. 



(b) 



(c) 



