THE THORAX 



o8i 



The inter auricular septum presents a slight depression, limited 

 inferiorly by a faint crescentic ridge, the concavity ot which is 

 directed upwards. These indicate the position of the foramen ovale 

 of the fcetal heart. 



Interior of the Left Ventricle. — ^The cavity of the left ventricle 

 extends quite to the apex of the heart, and is longer and narrower 

 than that of the right ventricle. It is somewhat conical, the base 

 being directed backwards and upwards. The interventricular 

 septum recedes from the cavity, and is concave towards it. In 

 transverse section, therefore, the left ventricle is oval, or nearly 

 circular. The wall of the left ventricle is about three times thicker 

 than that of the right, the difference being readily accounted for 



by the fact that the left ven- 

 tricle is concerned with the 

 systemic circulation, whilst 

 the right ventricle has to do 

 with the pulmonary circula- 

 tion, the latter involving a 

 much shorter circuit. The 

 wall of the left ventricle 

 attains its maximum thick- 

 ness about the junction of 

 the upper fourth and lower 

 three- fourths, and it is thin- 

 nest in the region of the 

 apex. The capacity of the 

 ventricle is about 4 ounces. 

 The portion of the cavity 

 immediately below the aortic 

 orifice is known as the aortic 

 vestibule, the walls of which 

 are fibrous. 



The left ventricle, like the 

 right, is provided with 

 columnae cameae. They are 

 arranged in a very intricate 

 manner, more particularly in 

 the region of the apex and over the posterior wall. The aortic 

 vestibule, and the interventricular septum, at least over its upper 

 part, are destitute of columnse cameae, and present a smooth 

 appearance. The musculi papillares are much larger than those 

 in the right ventricle ; they are two in number, anterior and pos- 

 terior ; and they are attached by their bases to the respective walls 

 of the ventricle, whilst their free ends are connected with the 

 chordae tendineae. 



The openings connected with the left ventricle are two in number, 

 namely, auriculo-ventricular and aortic. They are situated at 

 the base of the ventricle in close proximity to each other, and are 

 guarded b}^ important valves. The auriculo-ventricular orifice is 



Interventricular Sepium Ventricle 



Fig. 402. — Transverse Sections of 

 THE Heart. 



A, Through Apex (Superior View): 



B, Through Ventricles (Inferior Vie.v). 



