72 THORAX 



anterior angle, and between the two orifices is a strong and 

 rounded muscular ridge, the supra -ventricular ridge. This 

 projects into the cavity converting it into a U-shaped tube 

 which commences posterior to and below the supra-ventricular 

 ridge, runs anteriorly and to the left, towards the apex, and 

 turns upwards and anteriorly, along the anterior part of the 

 inter-ventricular septum and anterior to the supra-ventricular 

 ridge, to the orifice of the pulmonary artery. 



On transverse section 

 the cavity of the right ven- 

 tricle is semilunar in outline, 

 in consequence of the thick 

 ML V " Y!i " '' '^Sl inter - ventricular septum, 



Ms HBfHHft which forms the left and 



posterior wall, bulging into 

 the cavity (Fig. 37). Its 

 walls are much thicker 

 than the walls of the right 

 FIG. 37. Transverse section through atrium, but much thinner 

 the Ventricular Part of the Heart than the walls of the left 

 seen from above. (From Luschka. ) ventricle (Fig. 41). The 



1. Cavity of right ventricle. reason for these differences 



2. Cavity of left ventricle. i s obvioUS : the auricle has 



:: SSSr.SEuL mere 'y to force the blood 



5. Thinner wall of right ventricle. through the wide atHO- 



6. Inferior longitudinal (inter -ven- ventricular Orifice into the 



tncular) sulcus with middle cardiac , , , , j .i_ u*. 



vein and inferior branch of right right Ventricle, and the right 



coronary artery. Ventricle has Only tO SClld 



7. Anterior longitudinal (inter- ven- the blood through the lungS 



tncular; sulcus with great cardiac , , - . , 



vein and anterior branch of left tO the left atrium ; but the 



coronary artery. left ventricle has tO force 



the blood through the whole 



of the body, 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, 

 but the inner surface of the walls of the remaining part of the 

 ventricle is rendered extremely irregular by the projection of 

 a lace-work of fleshy ridges called trabecula carnecz. Some 

 of the trabeculse are merely ridges raised in relief upon the 



