ON THE LYMPHATICS. 351 



portal canals, and give off vaginal and interlobular veins, and the latter 

 terminate in the lobular venous plexus of the lobules of the liver. The 

 portal vein within the liver receives the venous blood from the capillaries 

 of the hepatic artery. 



PULMONARY VEINS. 



The pulmonary veins, four in number, return the arterial blood from 

 the lungs to the left auricle of the heart ; they differ from the veins in 

 general, in the area of their cylinders being very little larger than that of 

 the corresponding arteries, and in accompanying singly each branch of the 

 pulmonary artery. They commence in the capillaries upon the parietes 

 of the intercellular passages and air-cells, and unite to form a single trunk 

 for each lobe. The vein of the middle lobe of the right lung unites with 

 the superior vein, so as to form the two trunks which open into the left 

 auricle. Sometimes they remain separate, and then there are three pul- 

 monary veins on the right side. The right pulmonary veins pass behind 

 the superior vena cava to the left auricle, and the left behind the pulmo- 

 nary artery; they both pierce the pericardium. Within the lung the 

 branches of the pulmonary veins are behind the bronchial tubes, and those 

 of the pulmonary artery in front ; but at the root of the lungs the veins are 

 in front, next the arteries, and then the bronchi. There are no valves in 

 the pulmonary veins. 



CHAPTER VIII. 



ON THE LYMPHATICS. 



THE lymphatic vessels, or absorbents, have received their double appel- 

 lation from certain phenomena which they present ; the former name being 

 derivable from the appearance of the limpid fluid (lympha, water) w r hich 

 they convey ; and the latter from their supposed property of absorbing 

 foreign substances into the system. They are minute, delicate, and trans- 

 parent vessels, remarkable for their general uniformity of size, for a knotted 

 appearance w y hich is due to the presence of numerous valves, for the fre- 

 quent dichotomous divisions which occur in their course, and for their 

 division into several branches immediately before entering a gland. Their 

 office is to collect the products of digestion and the detrita of nutrition, 

 and convey them into the venous circulation near the heart. 



Lymphatic vessels commence in a delicate network which is distributed 

 on the cutaneous surface of the body, on the various surfaces of organs 

 and throughout their internal structure ; and from this network the lym- 

 phatic vessels proceed, nearly in straight lines, in a direction towards the 

 root of the neck. In their course they are intercepted by numerous small, 

 spheroid, or oblong, or flattened bodies, lymphatic glands. The lymphatic 

 vessels entering these glands are termed vasa inferentia or afferentia., and 

 those which quit them, vasa efferentia. The vasa inferentia vary in num 

 ber from two to six, they divide at the distance of a few lines from the 

 gland into several smaller vessels, and enter it by one of the flattened sur- 



