82 



THORAX 



the pulmonary valve, one of the cusps is placed anteriorly and 

 the other two posteriorly. The cusps of the aortic valve are 

 stronger than the cusps of the pulmonary valve described on 

 p. 71^ but correspond with them in all details of structure. 



Before terminating his examination of the left ventricle 

 the dissector should note that the muscular wall of the 

 cavity is thickest a short distance from the atrio-ventricular 



Opening of coronary sinus 



Rieht atrium 

 Musculi pectinati 



Interatrial septum 

 / Part of right sinus of the aorta 



Left atrium 



Central 

 fibrous mass 

 Fibrous ring of 

 tricuspid orifice 

 Inferior cusp of 

 tricuspid valve 

 Medial cusp of 

 tricuspid valve 



Trabeculacarnea -. 



Interventricular 

 septum 



Lower left 

 . pulmonary vein 



Wall of left 

 -atrium 



Central 

 " fibrous mass 



Pars mem- 

 ~ branacea septi 



reat cardiac vein 

 Fibrous ring of 

 " mitral orifice 

 Posterior cusp 

 of mitral valve 

 Anterior cusp 

 of mitral valve 



Wall of left ventricle 



FIG. 41. Section of the Heart showing the Interventricular and Inter- 

 auricular Septa and the Fibrous Rings round the Orifices. 



orifice and thinnest at the apex, and he should examine the 

 inter-ventricular septum. 



The Inter-ventricular Septum. The inter-ventricular septum 

 is a musculo-membranous partition which separates the left 

 ventricle not only from the right ventricle, but also from the 

 lower part of the right auricle. In the greater part of its 

 extent the septum is thick and muscular, and is thickest below 

 and anteriorly, where it springs from the lower border of the 

 heart immediately to the right of the apex and opposite the 



