2i8 PRACTICAL ANATOMY. 



lying, in its course, between the oesophagus and trachea, in a bed of fatty connec- 

 tive tissue. In the lower part of the neck, cervical and thoracic cardiac branches 

 are given off to the cardiac plexus. A little lower are given off pulmonary 

 branches, called, from their distribution, anterior and posterior ; these supply the 

 lungs through the pulmonary gangliated plexus. CEsophageal branches from 

 the pneumogastric form the plexus gulae. The pneumogastric nerve leaves the 

 thorax by the oesophageal opening in the diaphragm, and sends branches to the 

 solar plexus, from which, possibly, all the abdominal organs receive pneumogas- 

 tric influence. This, however, is purely physiological speculation. 



On the left side, the pneumogastric nerve passes behind the left brachio- 

 cephalic vein and in front of the arch of the aorta. As it is crossing the arch it 

 gives off its recurrent laryngeal branch. This nerve passes to the outer side of 

 the ductus arteriosus and gains the side of the left bronchus and trachea. The 

 inferior or recurrent laryngeal nerves supply branches to the trachea, oesophagus, 

 and to all the intrinsic muscles of the larynx except the crico-thyroid muscle. 



The coronary arteries supply the heart. They are given off from the ascend- 

 ing aorta. They embrace at their origin the common pulmonary artery by their 

 divergence. (Fig. 153.) Blood is returned from the heart by two sources : (i) 

 By minute veins which end in the foramina of Thebesius in the right auricle of the 

 heart. (2) Numerous veins come together to form the great coronary sinus. 

 This sinus opens into the right auricle of the heart, between the auriculo- 

 ventricular opening and the ascending vena cava. You will demonstrate this 

 opening, and also the valve, called the coronary, on your dissection. 



The Right Auricle of the Heart. Cut through the wall of the auricle from 

 the ascending to the descending vena cava in a direction from above downward. 

 Now, having thoroughly washed the parts, you will see : (i) The appendix auri- 

 cula, and (2) the atrium, sinus, or principal cavity of the auricle. In the atrium 

 see and locate: (i) The fossa waits, surrounded by a rim called the annnlns 

 ovalis; (3) the caval and auriculo-ventricular openings (Fig. 154); (4) the coro- 

 nary valve or valve of Thebesius and the RustacJiian valves, -at the respective 

 openings for the coronary sinus and ascending vena cava ; (5) the musculi pec- 

 tinati, which you will see on cutting through the appendix auriculae. These latter 

 are mechanical devices for giving strength to the walls of the auricle, analogous 

 to the chordae tendineae in the ventricles. 



The Semilunar Valves (Fig. 154). Cut into the aorta and pulmonary 

 artery an inch above where they leave the heart, and demonstrate these valves. 

 Fill the vessels with water and show the action of these valves in preventing 

 regurgitation. In the central point of each free margin of the valve find the 

 corpus Arantius. This is a mechanical device, whereby the valves occlude more 

 perfectly. Also find in the aorta the sinuses of Valsalva, or aortic sinuses, oppo- 

 site to which are found the attached margins of the valves. Above the fret 

 margin of the valves find the coronary arteries, left and right, given off from tin 

 aorta. 



The auriculo-ventricular valves, right and left, guard the respective open- 

 ings between the auricles and ventricles. Cut into the right ventricle (Fig. i 54) 

 and study the mechanical devices known as columnar carneae and chorda ten- 

 dineae ; also the left ventricle study in the same manner. 



The septa are : (i) The interauricular. In this you see the fossa ovalis. In 

 the foetus this was a communication between the auricles, called the forumei 

 ovale. It is in the posterior wall of the right auricle. (2) The interventricular, 

 separating the ventricles. 



Steps in Adult Circulation. ( i ) Blood is taken from below the diaphragm 

 by the inferior vena cava, and from above the diaphragm by the descending 

 \vna cava, to the right auricle of the heart. (2) Blood flows from the right 



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