Chap. 16 CONDUCTION AND COORDINATION NERVOUS SYSTEM 



303 



Arachnoid 

 trabecula 



Arochnoid 

 memb'one. 



Cerebrol 

 vein. 



Pia maler. 



^«o »A Feri'vQSCL/lgr 

 ^ spoce. 



L'Hinq cells of 



perivascular 



space. 



Copil'ory wilhm 

 pencopillory 

 spoce - 



Fig. 16.20. Diagram of the relations of the pia mater, the arachnoid and the 

 blood vessels of the brain. The pia mater dips into the channels of the larger 

 blood vessels. This figure shows the possibilities of broken blood vessels that create 

 hemorrhage of the brain. (After Weed. Courtesy, Ham: Histology, ed. 2. Phila- 

 delphia, J. B. Lippincott Co., 1953.) 



cerebellum, and (5) medulla. Each of them is the location of sense organs 

 and controls for which it is nicknamed: endbrain, "nose brain"; midbrain, 

 "eye brain"; medulla, "ear brain." From the fishes onward through the 

 mammals these sense organs are located according to this plan. In higher 

 animals the main parts that develop from the fundamental regions are as 

 follows : 



1. Endbrain. In fishes, this region is practically limited to the sense of 

 smell, whereas in mammals this sense is relatively little developed. In mam- 

 mals, the corpora striata have a stabiUzing effect upon the muscles in walk- 

 ing. In man, the cerebrum overtops the rest of the brain and its cortex is a 

 supreme achievement of the human species (Figs. 16.17, and 16.21). 



2. Between brain. This is the main pathway of the fibers between the 

 spinal cord and the cortex of the cerebral hemispheres, and by means of it 

 all other parts of the brain and the body are connected with the higher cen- 

 ters of control. The main substance of the between brain is in the side walls 

 of the third ventricle which are collectively called the thalamus. So called by 

 certain early anatomists who believed the enclosure to be a room in which 

 vital spirits were imparted to the optic nerves. The thalamus is the anterior 

 end of the primitive brain stem, the oldest part of the brain, a center of the 

 autonomic nervous system, and such functions as temperature regulation 

 and the awareness and expression of emotions (Fig. 16.21). 



3. Midbrain. The midbrain is a small part that connects larger ones. Its 

 floor is a part of the brain stem, very old in evolution. In fishes, the mid 

 brain is the original eye brain. In mammals, the four-fold bodies (corpora 

 quadrigemina) in its roof are, in a limited way, centers of visual and audi- 

 tory reflexes. 



