MAMMALIA 



289 



eral veins emptying into the left upper cavity known as 

 the left auricle and then goes to the left ventricle, which 

 by contraction of its walls propels the blood through 

 the aorta and its 

 branches to all 

 parts of the body. 

 The membranous 

 valves, held by 

 white glistening 

 cords, between the 

 auricles and ven- 

 tricles prevent the 

 backward flow of 

 the blood. 



The nerves are 

 the white glisten- 

 ing cords extend- 

 ing along with the 

 blood vessels and 

 giving off numer- 

 ous branches to the 

 muscles and other 

 structures. They 

 are connected 

 either with the 

 spinal cord or the 

 brain. Those 

 nerves which cariy sense stimuli, such as sound or a pin 

 prick to the brain or spinal cord, are called sensory nerves, 

 while the others bearing impressions from the brain or 

 spinal cord to the muscles are termed motor nerves. The 



FIG. 326. Nerve cell from the brain ; a, processes 

 by which it communicates with other cells near by ; 

 ax, long process or axis cylinder terminating in the 

 tail end of the spinal cord ; n, nucleus. Enlarged 

 two Lundred diameters. From Davison's " Mamma- 

 lian Anatomy." 



