THORACIC CAVITY 65 



with a valve, but the orifices of the other tributaries of the 

 sinus are generally devoid of valves. 



Cardiac Nerves. The coronary plexuses, from which the 

 nerve supply of the heart is directly derived, are offshoots of the 

 superficial and deep cardiac plexuses, which will be dissected 

 later (pp. 85 and 100). The right coronary plexus is formed by 

 twigs from the superficial cardiac plexus which descend along 

 the pulmonary artery, and by additional fibres from the deep 

 cardiac plexus. It is distributed along the course of the right 

 coronary artery. The left coronary plexus, which accompanies 

 the artery of the same name, is derived from the deep 

 cardiac plexus. The nerves do not slavishly follow the 

 arteries ; they soon leave the vessels, and are ultimately 

 lost in the substance of the heart. Here and there ganglia 

 are developed in connection with them. 



Dissection. The chambers of the heart and the great vessels which 

 communicate with them should now be examined, as far as possible whilst 

 the heart is still in situ, so that the relations of the various orifices to 

 the sternum and costal cartilages can be verified. Examine first the right 

 atrium and the venae cavse, then the right ventricle and the pulmonary 

 artery, and afterwards the left ventricle and the ascending part of the 

 aorta, which springs from it. The examination of the left atrium, and 

 the terminations of the pulmonary veins, cannot be conveniently undertaken 

 until the heart and the pericardium have been removed from the body 

 (see p. 89). 



Atrium Dextrum (O.T. Right Auricle). Open the right 

 atrium by means of the following incision. Enter the knife 

 at the apex of the auricle (O.T. auricular appendix) and carry 

 it posteriorly, close to the upper border of the auricle, across 

 the sulcus terminalis and through the lateral wall of the atrium, 

 to the posterior border of the lower end of the superior vena 

 cava; then downwards, posterior to the sulcus terminalis, to the 

 inferior vena cava ; and finally anteriorly, across the lower end 

 of the sulcus terminalis and above the anterior aspect of the 

 lower end of the inferior vena cava, to the coronary sulcus. 

 Throw the flap thus formed anteriorly, and clean the interior 

 of the cavity with a sponge. 



As the flap is turned anteriorly a vertical muscular bundle 

 will be noted on its inner surface. This is the crista terminalis, 

 which corresponds in position with the sulcus terminalis on 

 the outer surface. It marks the boundary between the 

 anterior part, the atrium, and the posterior part, which 

 is known as the venous sinus because the great veins of 



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