57 6 TEXT-BOOK OF PHYSIOLOGY 



The fillet ox lemniscus, consisting of. fibers having their origin partly from 

 the cells of the cuneate and gracile nuclei and partly from the cells of the 

 sensor end-nuclei of the spinal and various sensor cranial nerves, occupies 

 a region in the ventral and mesial portion of the tegmentum throughout its 

 entire extent. Superiorly this mesial fillet terminates for the most part 

 around nerve cells in the nuclei of the thalamus. From these nuclei new 

 fibers arise which pass for the most part to the cortex of the post-central 

 and parietal gyri. The fibers coming from the sensor end-nucleus of the 

 auditory nerve (the lateral fillet) lie on the lateral aspect of the pons and 

 crus. Superiorly they terminate in the post-geminum (the inferior quadri- 

 geminal body) and in the internal geniculate body. From these nuclei the 

 fibers composing the auditory tract pass to the super-temporal convolution. 



The medial longitudinal bundle, an upward extension of the fibers com- 

 posing a portion of the ground bundle of the spinal cord, is located on 

 either side of the median line just beneath the floor of the fourth ventricle and 

 the aqueduct of Sylvius. As it passes upward collateral branches are given 

 off, some of which arborize around the cell nuclei of the third, fourth, and 

 sixth cranial nerves of the same side, while others cross the median line and 

 arborize around the corresponding cell nuclei of the opposite side. Supe- 

 riorly some of the fibers become related to cells in the thalamus and sub- 

 thalamic region. This bundle of fibers appears to be mainly commissural in 

 character. 



The transverse fibers of the isthmus are found in the pons. The fibers 

 of the ventral as well as those of the more dorsal regions have their origin 

 in nerve-cells in the cortex of the cerebellum. From their origin they pass 

 through the cerebellar white matter, and through the middle peduncle as 

 far as the median line, where they decussate with fibers coming from the op- 

 posite side. Beyond this point they pass to the cerebellar cortex. From 

 their anatomic relations it is probable that these transverse fibers are com- 

 missural in character, bringing into relation opposite but corresponding 

 regions of the cerebellar cortex. In addition to the commissural fibers other 

 transverse fibers associate the cerebellar cortex with the gray matter in the 

 pons on both the same and opposite sides. In this way the cerebellum is 

 brought into relation with longitudinal fibers coming from and going to the 

 cerebrum. 



FUNCTIONS OF THE MEDULLA OBLONGATA, ISTHMUS, CORPORA 

 QUADRIGEMINA, AND BASAL GANGLIA 



Microscopic examination of the white and gray matter of these various 

 parts of the central nerve system shows that they are composed of nerve- 

 cells and nerve-fibers which morphologically do not differ in essential respects 

 from those found in the spinal cord, though their arrangement is far more 

 complicated and involved. The functions of these closely related structures 

 are in consequence equally complex and involved and but imperfectly known. 



In a general way it may be said that by virtue of the presence of nerve- 

 cells and definite tracts of nerve-fibers these structures collectively may be 

 regarded as consisting: 



1. Of nerve centers each of which has a special function, and 



2. Of conducting paths by which these centers are brought into relation 





