36 MANUAL FOR STABLE SERGEANTS. 



all other parts of the body it is^ collected by the thoracic duct; both 

 vessels emptying their lymph into the anterior vena cava just in 

 front of the heart. 



81. Lymph glands are small groups of cells through which the 

 lymph vessels pass and in which white corpuscles are formed. They 

 also act as filters for the removal of disease germs and other injurious 

 substances. ' 



82. Lymph is a watery fluid by which the tissues are nourished, 

 and by which waste material is gathered from them and eliminated. 

 Lymph is derived from the blood and passes into the tissues by oozing 

 through the thin walls of the capillaries. After bathing and nourish- 

 ing the tissues it is conveyed by the lymph vessels back to the blood, 

 again. The flow of lymph is brought about by the contraction of the 

 muscles in the vicinity of the vessels. 



83. Chyle is a milky fluid formed in the intestines. It contains 

 the nutritive elements of the food and is conveyed by a series of 

 lymph vessels to the blood. 



The Nervous System. 



84. The nervous system is divided into two minor systems, the 

 cerebrospinal, which is to a considerable extent influenced by the 

 will of the animal, and the sympathetic, over which the will has no 

 control. 



85. In the cerebrospinal system the central portion is composed 

 of two parts; the brain, which, occupies the cranial cavity, and the 

 spinal cord, which occupies the canal in the vertebrial column. 

 The communicating portion of this systena consists of the cerebro- 

 spinal nerves, which leave the brain and spinal cord in symmetrical 

 pairs and are distributed to the voluntary muscles and the organs 

 of common sensation and special sense. 



86. In the sympathetic system the central portion consists of a 

 double chain of ganglia (groups of nerve cells) connected by nerves, 

 which extends from the head to the tail below and on each side of 

 the spinal column. The communicating portion of this svstem is 

 distributed to the involuntary muscles, mucous membranes, internal 

 organs, and blood vessels. 



87. A nerve consists of a bundle of tubular fibers, held together 

 hy connective tissue. The nerve fibers are simply transmission 



