MANUAL FOR STABLE SERGEANTS. 3& 



right atrium throu,2:h the anterior and posterior venae cavae to be again 

 sent to the lungs for purification. 



76. The aorta is the beginning of the arterial system. It i& 

 given off at the base of the left ventricle and divides into thoracic and 

 abdominal parts. 



(a) The thoracic aorta passes forward and divides into branches 

 which supply the front part of the thorax, the front limbs, the necky 

 and the head. 



(b) The abdominal aorta passes upward and backward, below the 

 spinal column, to the last lumbar vertebrae where it divides into 

 four branches which are distributed to the hind quarters and posterior 

 limbs. Between its origin at the base of the left ventricle and its 

 termination in the lumbar region it gives off branches to the muscles 

 of the ribs, the lungs (for their nourishment), liver stomach, spleen^ 

 pancreas, intestines, kidneys ^ and muscles of the loins. 



77. (a) The anterior vena cava, a large, short vein, returns the 

 blood from the parts supplied by the thoracic aorta. It is located in 

 the front part of the thorax and empties its blood into the right 

 atrium. 



(b) The posterior vena cava, the largest and longest vein in the body^ 

 returns the blood from the parts supplied by the abdominal aorta. 

 It commences at the entrance of the pelvic cavity, runs forward under 

 the bodies of the vertebrae, and empties its blood into the right 

 atrium along with that from the anterior vena cava. 



78. The contraction of the heart sends the blood out in waves and 

 causes a temporary increased distention of the walls of the arteries. 

 These waves pass from the heart toward the extremities and can be 

 felt where the arteries are near the surface. The waves, or beats, 

 are called the pulse and correspond to the contractions of the heart. 

 The normal pulse rate is from 36 to 40 beats a minute. 



The Lymphatic System, 



79. The lymphatic system consists of a series of vessels, a num- 

 ber of glands through which the vessels pass, and certain fluids known 

 as lymph and chyle. 



80. The lymph vessels are thin, delicate tubes, similar to veins, 

 which gather the lymph from the tissues and convey it to the blood. 

 The lymph from the right fore extremity, thd right side of the head, 

 neck, and thorax, is collected by the right lymphatic vessel. From 



