I054 ^ MANUAL OF ANATOMY 



(i) the upper, middle, and lower cervical cardiac branches of the right sym- 

 pathetic ; (2) the upper and lower cervical cardiac branches of the right 

 pneumogastric ; (3) one or two branches from the right recurrent laryngeal 

 nerve ; and (4) one or two thoracic cardiac branches from the right pneumo- 

 gastric nerve. The contributory nerves to the left half of the plexus are 

 (i) the middle and lower cervical cardiac branches of the left sympathetic ; 



(2) the upper cervical cardiac branch of the left pneumogastric ; and 



(3) branches from the left recurrent laryngeal nerve. As regards the upper 

 cervical cardiac branch of the left sympathetic, and the lower cervical cardiac 

 branch of the left pneumogastric, they have already been followed over the 

 arch of the aorta into its concavity, where they have been seen to form the 

 superficial cardiac plexus. The connection between the two halves of the 

 deep cardiac plexus is to be made out, as well as that between the right half 

 and the superficial cardiac plexus. The right coronary plexus is to be shown 

 coming from the superficial and right half of the deep cardiac plexus. From 

 the right half of the deep cardiac plexus branches are to be looked for passing 

 to the right anterior pulmonary plexus, and also to the right auricle. The 

 left coronary, plexus is to be shown coming from the left half of the deep 

 cardiac plexus, of which it forms the chief prolongation. Branches are also 

 to be looked for passing to the left anterior pulmonary plexus, and to the 

 left auricle. 



The heart is now to be removed by dividing the trunk of the pulmonary 

 artery and the pulmonary veins. The aorta and pulmonary artery are, in 

 succession, to be attached to a water-tap, and by turning the stop-cock the 

 flow of water will demonstrate the action of the arterial valves. The three 

 bulgings on the exterior of each vessel close to the corresponding ventricle, 

 and produced by the sinuses of Valsalva in the interior, will be at the same 

 time shown. The auricular portion of the heart should now be separated 

 from the ventricular portion. There is no continuity between the auricular 

 and ventricular muscular fibres, these being only connected through the 

 medium of the fibrous rings round the auriculo-ventricular orifices. A heart 

 usually requires to be boiled in the first place, in order to dissolve the fibrous 

 tissue, but the separation of the auricular from the ventricular portion is 

 possible by careful dissection. After its completion an instructive view will 

 be obtained of the orifices at the base of the ventricular portion. The auriculo- 

 ventricular orifices will be seen to lie side by side, the aortic orifice being in 

 front of and between them, and the pulmonary orifice being in front of the 

 aortic. In the angle between the auriculo-ventricular and aortic orifices a 

 collection of dense fibrous tissue, of the consistence of cartilage, will be found, 

 and processes are to be shown passing from it to the fibrous rings which sur- 

 round the auriculo-ventricular and aortic orifices. 



The pulmonary artery is next to be laid open by an incision passing between 

 two of the three segments of which the pulmonary valve is composed. The 

 segments of the valve and the sinuses of Valsalva are to be examined, but 

 these admit of much better observation in the case of the aortic valve. The 

 aorta is also to be laid open, observing the same precaution as in opening 

 the pulmonary artery, and the segments of the aortic valve are to receive 

 most careful attention. The two lunulae and corpus Arantii of each seg- 

 ment are to be noted, the direction of the free margins of the segments is to 

 be observed, and the sinuses of Valsalva are to be looked to. The orifices 

 of the right and left coronary arteries are to be examined, that of the right 

 being connected with the right antero-lateral sinus of Valsalva, and that of 

 the left with the left antero-lateral sinus of Valsalva. Lastly, the function 

 of the aortic and of the pulmonary valves is to be carefully studied. 



For the purpose of examining the arrangement of the muscular fasciculi 

 of the auricles and ventricles a sheep's heart may be obtained and boiled 

 for a short time in order to dissolve the fibrous tissue. 



Posterior Mediastinum. — The thoracic part of the trachea is now to be 

 dissected, and its bifurcation into two bronchi, right and left, is to be shown, 

 as well as some bronchial glands which lie within the angle of bifurcation. 

 The greater size of the right bronchus and the greater length of the left 



