158 THE CEREBRUM: 



successive strands which end in the opposite motor nuclei of the 

 cerebral nerves. The function of this latter part is reflex. 



(2) The descending part of the medial longitudinal bundle 

 is composed chiefly of uncrossed axones from the large cell- 

 bodies in the nuclei of the reticular formation. Beginning at the 

 nucleus lateralis superior in the mid-brain, it receives fibers 

 from each reticular nucleus down to the nucleus lateralis inferior 

 of the medulla. It receives the largest accession of fibers in the 

 pons, where the nucleus lateralis medius and the three nuclei 

 centrales are located. On this account James S. Collier suggests 

 that it be called the medial ponto-spinal tract. It has been traced 

 through the anterior fasciculus proprius to the lower part of the 

 spinal cord. Its size is gradually reduced by the ending of a few 

 fibers in the gray substance corresponding to each segment of the 

 cord. 



In the mid-brain the medial longitudinal bundle also contains 

 fibers derived (i) from the oculomotor nucleus, which descend 

 to the pons, and enter into facial nerve through which they supply 

 the muscles of expression above the eye; and (2) from the nucleus 

 of the abducent nerve. Running upward and decussating, the 

 latter strand of fibers terminates in the opposite nucleus of the 

 oculomotor nerve, and thus innervates the internal rectus of that 

 eye. This strand accounts for the conjugate action of the two 

 eyes in both health and disease. 



The anterior longitudinal bundle forms a distinct strand 

 situated in the formatio reticularis ventro-lateral to the medial 

 longitudinal bundle (Figs. 47 and 48). It degenerates downward 

 and is a descending tract. It takes its origin hi the superior 

 colliculus of the corpora quadrigemina, whence it decussates at 

 once through the dorsal tegmental decussation (Meynerti) and 

 descends through the reticular formation of the pons and medulla ; 

 and!, then, through the fissural side of the anterior column of the 

 spinal cord until it fades away in the lumbar region. Only by 

 its degeneration has it been located. Its fibers end in the gray 

 matter of the cord on both sides and in the genetic nuclei of cere- 

 bral nerves; but, chiefly, in the nuclei of the oculomotor, trochlear 

 and abducent nerves and in the cilio-spinal center of the spinal 



