44 



DISSECTION OF THE DOG 



to the wall of the chest, the surface follows the curve of the ribs and is, therefore, 

 convex dorso-ventrally. When the lungs have been satisfactorily hardened 

 by preservative before the chest is opened, the surface is generally marked 

 by grooves which indicate the position of the ribs. 



The medial or mediastinal surface (facies mediastinalis) is of much smaller 

 extent owing to the fact that the diaphragm encroaches more upon the thorax 

 medially than laterally. The presence of the heart produces a deep depression 

 on this face. Immediately dorsal to the depression for the heart is the hilus 



Fig. 17. — Lateral surface of tie left lung. 



pulmonis — that is, the point of attachment of the root. Cranial to the cardiac 

 depression, each lung, if well hardened, shows a curved groove for the internal 

 mammary artery. Though these are the general features of the mediastinal 

 surface, there are certain points of dissimilarity in the two lungs. In addition 

 to the cardiac depression, the left lung possesses a deep groove, dorsal to the 

 hilus and the pulmonary ligament, in which lies the aorta. The rest of the 

 surface is flattened. 



The mediastinal surface of the right lung has an extensive cardiac depression, 

 in the formation of which the intermediate lobe plays a part. Running from 

 the neighbourhood of the lung apex is a broad groove for the cranial vena cava ; 

 and dorsal to the hilus there is a deep, slightly curved channel connected with 

 the groove for the vena cava. The second of these grooves is produced 

 by the vena azygos. Caudal to the lung root and partly formed by the 



