ANATOMY. 37 



vessels from the remainder of the body unite in a trunk called the 

 thoracic duct, which begins in the lumbar region, passes forward 

 beneath the lumbar and dorsal vertebrae, and empties into the anterior 

 vena cava just in front of the heart. 



Each of the villi of the intestines contains a minute vessel called 

 a lacteal, which absorbs chyle and receives its name from the lacteal 

 or milky appearance of that fluid. These vesesls of the smaller lym- 

 phatic system unite and form larger tubes which empty into the 

 recejrtaculum chyli (chyle reservoir), which is a part of the thoracic 

 duct of the larger system. 



It will thus be seen that the lymph with its waste material and 

 the chyle with its nutrient material are mixed and poured into the 

 impure blood. The lymph and chyle are taken up into the serum 

 and the waste material is thrown off from the circulating blood by 

 the lungs, skin, and kidneys. 



Lymph, therefore, makes a circuit very much as blood does. 



To simplify the explanation of the system, the lymphatic glands 

 have not been mentioned. 



Glands are organs, the function of which is to separate certain 

 substances from the blood, which are either to be used in the animal's 

 system or to be thrown off as waste material. 



The lymphatic glands are so placed that the lymphatic vessels 

 pass through them in their course toward the main trunks. These 

 glands act as niters and remove any infective material from the 

 lymph and also supply lymph corpuscles, which are identical with 

 the white corpuscles of the blood. 



When the glands are situated near diseased structures, an amount 

 of infected material lodges in the glands, greater than can be over- 

 come by the lymph corpuscles, and, in consequence, inflammation 

 and swelling of the glands result. 



ANATOMY OF THE NERVOUS SYSTEM. 



A nerve consists of" a bundle of tubular fibers, held together by 

 dense connective tissue; the nerve fibers form a conducting appara- 

 tus, to convey impulses of sensation and to transmit impulses of 

 motion. 



The nervous system is divided into two minor systems, the cerebro- 

 spinal, which is to a considerable extent influenced by the will of 

 the animal, and the sympathetic, which is not directly influenced by 

 the will. 



In the first the center is made up of two portions, the brain and 

 the spinal cord. 



The brain is situated in the cranial cavity; the spinal cord is 

 elongated and continuous with the brain and is situated in the canal 

 of the vertebral column. 



