THE NERVOUS SYSTEM. 303 



THE INTERNAL STRUCTURE OF TPIE PONS VAROLII. 



On cross-section the pons is seen to consist of a dorsal 

 teg mental part, and a ventral part, or crusta. 



The crusta is composed of transverse fibres (fibres from the 

 cerebellum to the pons and from the nucleus pontis to the cere- 

 bellum), which go to form the middle cerebellar peduncles; lon- 

 gitudinal fibres, which belong to the pyramidal tracts, much scat- 

 tered ; and gray matter, which here forms a nucleus called the 

 nucleus pontis. 



The tegmentum of the pons contains a thick layer of gray 

 matter, which forms the floor of the fourth ventricle, and from 

 which cranial nerves take their origin; formatio reticularis, 

 which is the continuation upward of the same from the cord; 

 the superior olivary nucleus ; the posterior longitudinal bundle ; 

 the fillet; the superior cerebellar peduncle; and the corpus 

 trapezoides. 



The fillet occupies a position between the crusta and tegmen- 

 tum, and to differentiate it from a tract that makes its appear- 

 ance above the nucleus of the third nerve is called the me- 

 sial fillet. 



The other tract is named the lateral fillet. 



The lateral fillet is composed of longitudinal fibres which 

 take origin from the nucleus of the eighth cranial nerve (coch- 

 learis) of the same side, from that of the opposite side, and 

 from the superior olive. They end in the inferior quadri- 

 geminal body, the internal geniculate body, and a few in the 

 superior quadrigeminal body. 



The mesial fillet has been described. It takes its origin in 

 the medulla from the cuneate and gracile nuclei of the opposite 

 side. Some of its fibres end in the superior quadrigeminal body, 

 but the remainder pass through the subthalamic tegmental 

 icuion into the posterior part of the lateral nucleus of the optic 

 thalamus. Some end here, while some are continued through 

 the thalamus, enter the corona radiata, and pass to the posterior 

 central gyrus of the Eolandic region. 



THE STRUCTURE OF THE CEREBELLUM. 



On section the gray matter of the cerebellum is found to 

 occupy the cortex; to its arborescent appearance the term arbor 

 vitoe has been applied. 



The white matter of each hemisphere contains a nucleus of 

 gray matter: the corpus dentatum. 



The middle peduncles connect the cerebellum with the pons. 



