1100 SPLANCHNOLOGY 



Vessels and Nerves. The pulmonary artery conveys the venous blood to the lungs; it divides 

 into branches which accompany the bronchial tubes and end in a dense capillary net-work in 

 the walls of the alveoli. In the lung the branches of the pulmonary artery are usually above 

 and in front of a bronchial tube, the vein below. 



The pulmonary capillaries form plexuses which lie immediately beneath the lining epithe- 

 lium, in the walls and septa of the alveoli and of the infundibula. In the septa between the 

 alveoli the capillary net-work forms a single layer. The capillaries form a very minute net-work, 

 the meshes of which are smaller than the vessels themselves; their walls are also exceedingly 

 thin. The arteries of neighboring lobules are independent of each other, but the veins freely 

 anastomose. 



The pulmonary veins commence in the pulmonary capillaries, the radicles coalescing into 

 larger branches which run through the substance of the lung, independently of the pulmonary 

 arteries and bronchi. After freely communicating with other branches they form large vessels, 

 which ultimately come into relation with the arteries and bronchial tubes, and accompany 

 them to the hilus of the organ. Finally they open into the left atrium of the heart, conveying 

 oxygenated blood to be distributed to all parts of the body by the aorta. 



The bronchial arteries supply blood for the nutrition of the lung; they are derived from the 

 thoracic aorta or from the upper aortic intercostal arteries, and, accompanying the bronchial 

 tubes, are distributed to the bronchial glands and upon the walls of the larger bronchial tubes 

 and pulmonary vessels. Those supplying the bronchial tubes form a capillary plexus in the 

 muscular coat, from which branches are given off to form a second plexus in the mucous coat; 

 this plexus communicates with small venous trunks that empty into the pulmonary veins. 

 Others are distributed in the interlobular areolar tissue, and end partly in the deep, partly 

 in the superficial, bronchial veins. Lastly, some ramify upon the surface of the lung, beneath 

 the pleura, where they form a capillary network. 



The bronchial vein is formed at the root of the lung, receiving superficial and deep veins corre- 

 sponding to branches of the bronchial artery. It does not, however, receive all the blood supplied 

 by the artery, as some of it passes into the pulmonary veins. It ends on the right side in the 

 azygos vein, and on the left side in the highest intercostal or in the accessory hemiazygos vein. 



The lymphatics are described on page 718. 



Nerves. The lungs are supplied from the anterior and posterior pulmonary plexuses, formed 

 chiefly by branches from the sympathetic and vagus. The filaments from these plexuses accom- 

 pany the bronchial tubes, supplying efferent fibers to the bronchial muscle and afferent fibers 

 to the bronchial mucous membrane and probably to the alveoli of the lung. Small ganglia 

 are found upon these nerves. 



THE DIGESTIVE APPARATUS (APPARATUS DIGESTORIUS; ORGANS 



OF DIGESTION). 



The apparatus for the digestion of the food consists of the digestive tube and of 

 certain accessory organs. 



The Digestive Tube (alimentary canal) is a musculomembranous tube, about 

 9 metres long, extending from the mouth to the anus, and lined throughout its 

 entire extent by mucous membrane. It has received different names in the various 

 parts of its course: at its commencement is the mouth, where provision is made 

 for the mechanical division of the food (mastication), and for its admixture with 

 a fluid secreted by the salivary glands (insalivatiori) ; beyond this are the organs 

 of deglutition, the pharynx and the esophagus, which convey the food into the 

 stomach, in which it is stored for a time and in which also the first stages of the 

 digestive process take place; the stomach is followed by the small intestine, which 

 is divided for purposes of description into three parts, the duodenum, the jejunum, 

 and ileum. In the small intestine the process of digestion is completed and the 

 resulting products are absorbed into the blood and lacteal vessels. Finally the 

 small intestine ends in the large intestine, which is made up of cecum, colon, rectum, 

 and anal canal, the last terminating on the surface of the body at the anus. 



The accessory organs are the teeth, for purposes of mastication; the three pairs 

 of salivary glands the parotid, submaxillary, and sublingual the secretion from 

 which mixes with the food in the mouth and converts it into a bolus and acts 

 chemically on one of its constituents; the liver and pancreas, two large glands 

 in the abdomen, the secretions of which, in addition to that of numerous minute 

 glands in the walls of the alimentary canal, assist in the process of digestion. 



