DISSECTING MANUAL. 



the external branches are muscular; the internal are cutane- 

 ous, become superficial near the spines, and run directly out- 

 ward. Of the lower six the internal are muscular; the ex- 

 ternal are cutaneous, pierce the Latissimus dorsi at some 

 distance from the midline, and run downward and outward, 

 even to the buttock. [613] 



Sympathetic. The thoracic part consists of ten or eleven 

 (or less) irregular ganglia which are connected by commis- 

 sural cords, receive a white ramus communicans from each 

 thoracic nerve, and send one to each. Pulmonary branches 

 arise from the cord opposite the second, third, and fourth 

 ganglia, and join the posterior pulmonary plexus. Aortic 

 branches, from the upper five ganglia, supply the thoracic 

 aorta above. The great splanchnic nerve arises between the 

 fifth and ninth ganglia and descends through the posterior 

 mediastinum and cms of the diaphragm, developing a gan- 

 glion (great splanchnic). It supplies the esophagus and de- 

 scending thoracic aorta, and joins the (solar plexus) semilunar 

 ganglion. The small splanchnic nerve arises opposite the ninth 

 and tenth ganglia, descends on the spine, pierces the crus and 

 joins the solar plexus. The least splanchnic nerve arises from 

 the preceding, or the last ganglion, pierces the diaphragm 

 and joins the renal plexus. [708] 



THE HEART. 



The heart lies on the diaphragm, in the middle mediasti- 

 num, enclosed in the pericardium; its long axis is directed 

 downward, forward, and to the left. It is hollow and divided 

 by a septum into right and left halves, each consisting of an 

 upper and lower chamber, the auricle and ventricle respec- 

 tively. It is conical and irregularly flattened, with a base, 

 apex, two surfaces and two borders. A transverse groove 

 (auriculo-ventricular) indicates the separation between the 

 auricles and ventricles, a longitudinal groove (interventricu- 



[124] 



