THE THORAX 947 



root of the neck for about ij inches. It is here covered by the 

 dome of the pleura, and a Httle below its highest point it presents 

 a groove on its internal and anterior aspects. In the case of the 

 right lung this groove is produced by the innominate and right 

 subclavian arteries, and, in the case of the left lung, by the sub- 

 clavian artery of that side. Below this groove there is another 

 groove, produced on either side by the innominate and subclavian 

 veins. 



The base is extensive, semilunar in outline, and concave in adapta- 

 tion to the upper arched surface of the diaphragm, upon which it 



Two FoUides 



Trabecula 



Medulla 



Cortex 



Fig. 386. — Transverse Section of a Lobule of the Thymus Gland of 



A Kitten 



(The concentric corpuscles of Hassall are shown in the medulla). 



rests, with the intervention of the pleura. The base of the right 

 lung is related to the right lobe of the Uver, and that of the left 

 lung to the left lobe of the hver, the stomach, and the spleen, the 

 diaphragm intervening in each case. The margin of the base is 

 thin and sharp, and it extends into the costo-diaphragmatic space, 

 reaching lowest behind, but nowhere as low as the line of the costo- 

 diaphragmatic reflection of the pleura. 



The outer surface is extensive and convex, and in health it is 

 closely applied to the inner surfaces of the ribs and of the internal 

 intercostal muscles. 



The inner surface is of much more Umited extent than the outer. 



