SURFACES. 



157 



running along the median raphe just ventral to the central gray 

 substance. In Weigert-Pal sections it shows clearly as a dark 

 triangle nearly one-sixteenth of an inch on a side. The tract 

 will be found in the same relative position in the pons and medulla 

 oblongata. In addition to several very small strands 'of fibers 

 which will be explained later, the medial longitudinal bundle is 



Fig. 46. Transverse section through the corpora mammillaria and the superior 

 colliculi of the corpora quadrigemina. (Original.) 



a. Lateral geniculate body. b. Thalamus. c. Medial geniculate body. d. Brachium 

 superius. e. Pineal body. f. Stratum griseum centrale. g. Superior colliculus of corpora 

 quad. h. Formatio reticularis. i. Substantia nigra. j. Basis pedunculi. k. Medial and 

 lateral nuclei of corpus mammillare. 1. Ventral tegmental decussation (Foreli). m. Dorsal 

 tegmental decussation (Meynerti). n. Medial longitudinal bundle, o. Optic tract, p. Red 

 nucleus, q. Medial fillet. 



functionally composed of two tracts: (i) An ascending bundle; 

 and (2) a descending bundle. 



(i) The ascending part of the medial longitudinal bundle is 

 composed of fibers derived from the gray matter of the spinal 

 cord and from the terminal nuclei of sensory cerebral nerves. 

 It is the continuation of the long ascending fibers of the anterior 

 fasciculus proprius. Possibly a small portion of the tract runs 

 through the posterior commissure to the thalamus and is common 

 sensory in function ; but the major part of it decussates in several 



