THORACIC CAVITY 89 



usually provided with a valve ; the orifice of the small cardiac 

 vein may be provided with a valve, but the orifices of the 

 other tributaries of the sinus are generally devoid of valves. 



Nervi Cordis. The coronary plexuses, from which the 

 nerves of the heart are directly derived, are offshoots of 

 the superficial and deep cardiac plexuses. The superficial 

 cardiac plexus has already been investigated (p. 56). It 

 lies below the arch of the aorta and above the bifurcation 

 of the pulmonary artery, at the right side of the ligamentum 

 arteriosum. The deep cardiac plexus, which is situated 

 between the posterior surface of the arch of the aorta and 

 the front of the bifurcation of the trachea, will be dissected 

 later (p. 129). 



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 oTistributed along the course of the right 

 coronary artery. The left coronary plexus^ which accom- 

 panies 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 cavae, 

 then the right ventricle and the pulmonary artery, and after- 

 wards 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. 119). 



Open the right atrium by means of the following incision. 

 Enter the knife at the apex of the auricle of the atrium (O.T. 

 auricular appendix) and carry it backwards, 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, 

 forwards, across the lower end of the sulcus terminalis and 

 above the anterior aspect of the upper end of the inferior vena 

 cava, to the coronary sulcus. Throw the flap thus formed 

 forwards, and clean the interior of the cavity with a sponge. 



Atrium Dextrum (O.T. Right Auricle). As the flap 



