36 



VETERINARY STUDIES 



delicate, and fits closely to the brain substance — over the con- 

 volutions and into the depressions. 



Gray matter, folded into convolutions, covers the surface. 

 The interior is composed of white matter. 



Function. — The physiological function of the brain is to 

 receive messages, consider' information, and send out appro- 

 priate impulses or orders to the proper organs. 



Divisions.— The brain is divided for study into : (a) cerebrum ; 

 (b) cerebellum; (c) medulla; (d) isthmus. 



Fig. 21. — Spinal Cord and Brain in Diagram. (M. H. B.) 



1. Cross Section of the Spinal Cord. A, superior median fissure; B, in- 

 ferior median fissure; C, C, superior gray horns; D, D, inferior gray horns; 

 E, central canal; F, white substance. 



2. Vertical Mid-Section of Brain. A, medulla; B, cerebellum; C, pons or 

 bridge; D, isthmus; E, cerebrum. 



The cerebrum, is largest, and located in the anterior part 

 of the brain cavity, and is divided into two lobes or hemispheres 

 by the median fissure. 



The cerebellum, smaller than the cerebrum, is located in the 

 posterior and inferior part of the brain cavity, and consists of 

 three small lobes. Section shows the arbor- vifee (tree of life) 

 arrangement of nerve tissue. It is the function of the cerebellum 

 to control the voluntary muscles that they may work in harmony. 



The medulla is a continuation of the spinal cord and extends 

 from the occipital opening in the brain cavity to the pons or 

 bridge, and is located posterior and inferior to the cerebellum. 



Within the medulla are located a number of important centers, 

 among them the ones controlling respiration; the caliber of 

 blood vessels and distribution of the blood according to the 

 needs of the body; the center controlling the processes of swal- 

 lowing; the vomiting center; and the center controlling the 

 secretion of saliva. 



