650 PHYSIOLOGY. 



The ii'hite matter of the hemispheres consists of medullated 

 libers whose size is very various. As a rule, however, they are 

 smaller than those of the cord and bulb. For the most part, they 

 are arranged in bundles separated by layers of neuroglia. 



Central Ganglia of the Brain. At the level of the hilus of the 

 brain the cerebral peduncles sink into the body of the 'two hemi- 

 spheres. They contain fibers which proceed from the cord, pons, 

 and cerebellum to the brain, as well as those fibers which proceed 

 from the brain to the cord, pons, and cerebellum. There are also 

 direct fibers which reach from the peduncles to the brain cortex. 

 However, there are other indirect or ganglionic fibers which com- 

 municate previously in the nuclei or ganglia of the gray substance. 

 The ganglia referred to are : the optic thalami and the corpora striata. 

 The optic thalami are two oval bodies placed upon the tract of the 

 cerebral peduncles. At the posterior part of the thalamus are the 

 external and internal geniculate bodies. Between the pulvinar and 

 the origin of the pineal gland is found a small surface, slightly 

 depressed and of triangular form; it is the triangle of the habenula. 

 Within this triangle is a small prominence known as the nucleus of 

 the habenula. The habenula is the peduncle of the pineal gland. 



The inferior surface of the thalamus rests upon the cerebral 

 peduncle, from which it receives some fibers. In the rear it remains 

 free, and presents two nipplelike swellings: the geniculate bodies. 

 One lies internal; the other external. 



Monakow divides the nuclei of the thalamus as follows: (1) 

 anterior, (2) median, (3) ventral, (4) posterior, and (5) pulvinar. 

 The posterior root-fibers arborize about the nuclei of Goll and Bur- 

 dach. From there they are continued by a second neuraxon to end 

 in the ventral nucleus of the thalamus. 



Each thalamus has a double connection with all parts of the 

 cerebral cortex by neuraxons from its various nuclei to the cortex, 

 and by neuraxons from the pyramidal cells of all parts of the cortex. 

 The neuraxons of the ganglionic cell-layer of the retina end about 

 the cells of the pulvinar and external geniculate body, thus connect- 

 ing it with the primary division of the optic tract. It has also a 

 double connection with the occipital lobes by neuraxons from the 

 pulvinar cells (optic radiations), which terminate in the pyramidal 

 cells of the occipital cortex and by neuraxons from the pyramidal 

 cells of that lobe which end in the cells of the pulvinar. 



Corpora Striata, The corpora exist as two large ovoid gray 

 masses lodged within the thickness of the frontal lobe. They are 



