298 THE RHOMBENCEPHALON. 



corpora quadrigemina, to the lower part of the medulla; there it 

 approaches the medial longitudinal bundle and is continued along 

 the fissural surface of the anterior column in the cord. Its ter- 

 mination is in the central gray substance, chiefly the cilio-spinal 

 centers. It forms the middle link in the visual reflex arc. Its 

 bulbar and spinal portions constitute, chiefly, the pupillo-dilator 

 tract (see pages 158, 276 and 355). 



Longitudinal Fibers of the Lateral Area. The contents 

 of the lateral area (Figs. 92 and 93) are as follows: Superficially, 

 the lateral fasciculus proprius, the anterior descending, and the 

 anterior ascending cerebello-spinal tracts and the spino-thalamic 

 tract. Deeply, lies the substantia reticularis grisea. Imbedded 

 in the substantia reticularis are the nucleus ambiguus, the nucleus 

 lateralis inferior and the accessory olivary nuclei, and in the 

 fasciculus proprius is the main inferior olivary nucleus. The 

 gray matter of the substantia reticularis grisea is a part of the 

 disintegrated anterior columna of the cord and, unlike that of 

 the anterior area, it contains the bodies of many large nerve 

 cells. 



Lateral Fasciculus Proprius (Fasciculus Lateralis Pro- 

 prius, Figs. 93 and 94). The whole lateral column of the spinal 

 cord, except the lateral pyramidal and cerebello-spinal tracts, is 

 continued into the lateral area of the medulla. Composed of as- 

 cending and descending axones which are commissural and asso- 

 ciative for different segments of the spinal cord, the lateral fascic- 

 ulus proprius ascends into the lateral area of the medulla, and 

 runs in part beneath and in part superficial to the inferior olivary 

 nucleus; beyond the olive, it is continued in the substantia reticu- 

 laris grisea of the medulla and reticular formation of pons and 

 mid-brain. Among the fibers of the lateral fasciculus proprius, 

 ventral to the olive, is the triangular tract of Helwig and, dorsal 

 to the olive, the olivary bundle. The former is believed to rise in 

 the olive of the medulla and the latter to end in it. They are 

 made up of descending axones and, according to'Bechterew, form 

 a functionally continuous tract. 



The anterior descending cerebello-spinal tract (fasciculus 

 descendens cerebello-spinalis anterior) rises in the cerebellar ganglia 



