THORACIC CAVITY 



99 



walls of the left ventricle (Fig. 50). The reason for the 

 differences is obvious : the atrium has merely to force the 

 blood through the wide atrio-ventricular orifice into the right 

 ventricle, and the right ventricle has only to send the blood 

 through the lungs to the left atrium ; but the left ventricle 

 has to force the blood through the whole of the trunk, the 

 head and neck, and the limbs; and the muscular strength 

 of the walls of the cavities 

 of the heart is proportional 

 to the work they have to do. 

 The portion of the right 

 ventricle which ascends to 

 the orifice of the pulmonary 

 artery is the conus arteriosus. 

 Its walls are smooth and 

 devoid of projecting muscular 

 bundles (Fig. 49) ; but the 

 inner surface of the walls 

 of the remaining part of the 

 ventricle is rendered ex- 

 tremely irregular by the pro- 

 jection of a lace- work of 

 fleshy ridges called trabeculce 

 carnece. (Figs. 49, 53). Some 

 of the trabeculae are merely 

 ridges raised in relief upon 

 the surface ; others are at- 

 tached to the wall at each 

 extremity, but are free in 



the rest Of their extent. The coronary artery. 



cavity of the ventricle is 



invaded, however, not only by the trabeculae carneae, but 

 also by a number of conical muscular projections, the 

 musculi papillares. The papillary muscles are attached by 

 their bases to the wall of the ventricle, whilst their apices 

 are connected, by a number of tendinous strands, called chorda 

 tendinecB, to trie margins and the ventricular surfaces of the 

 cusps of the atrio-ventricular -valve: Asa fulfe ; there is one 

 large anterior jiLjii'lary muscle 'attached to rice' anterior wall, a 

 large inferior papillary muscle attached to the inferior wall, and 

 a number ,of smaller papillary muscles -a ttaclied to the septal 

 wall. Occasionally the anterior ana inferior muscles are repre- 

 ii 7 a 



FIG. 50. Transverse section through 

 the Ventricular Part of the Heart 

 seen from above. (From Luschka. ) 



1. Cavity of right ventricle. 



2. Cavity of left ventricle. 



3. Ventricular septum. 



4. Thick wall of left ventricle. 



5. Thinner wall of right ventricle. 



6. Inferior longitudinal (interventricu- 



lar) sulcus with middle cardiac 

 vein and interventricular branch 

 of right coronary artery. 



7. Anterior longitudinal (interventricu- 



lar) sulcus with great cardiac vein 

 and interventricular branch of left 



