62 Anatomy of the Nervous System 



descending fibres which convey to the motor columns of the 

 spinal cord the impulses received from the cerebellum- 

 impulses which are believed to be important factors in 

 muscular coordination and in the maintenance of muscle 

 tone. These fibres pass ventro-medially to cross the raphe 

 as the ventral tegmerUal decussation {fountain decussation of 

 Forel), after which they turn posteriorly, forming the rubro- 

 spinal tract {fascictdus ruhro-spinalis) in a position ventro- 

 medial to the red nucleus. Farther back than this nucleus, 

 the tract passes gradually in a lateral direction to a location 

 just ventral to the cauda of the brachium conjunctivum. 

 Papez describes its descending course in the rat as "medial 

 to the lateral lemniscus, ventral to the trigeminus, facial 

 nucleus, etc.". 



From the small-celled portions of the red nucleus, arise 

 crossed and uncrossed fibres to other parts of the tegmentum 

 and to the thalamus. From the latter, the impulses are 

 transmitted to the corpus striatum and cerebral cortex. As 

 a result of these relations, the small-celled region is found to 

 correspond in size with the degree of development of the 

 cerebellar hemispheres and of the cerebral cortex (especially 

 the frontal cortex), both of which are small in the rat. 



Dorsal to the ventral tegmental decussation and the 

 decussation of the superior cerebellar peduncles, is another 

 group of fibres crossing the raphe. These fibres arise in the 

 tectum, whence they curve round the central gray matter 

 to its ventral surface {fountain-like radiation of Meyn&rt) 

 and form the dorsal tegmental decussation {fountain decussation 

 of Meynert). They then turn directly posteriorly, just lateral 

 and ventral to the medial longitudinal bundle, as the tecto- 

 spinal tract, which has already been observed in the hind- 

 brain. Some of the fibres are said by certain authors not to 

 decussate but to pass posteriorly on the same side along with 

 the lateral lemniscus. After giving off fibres to the oculomotor 

 and trochlear nuclei, the tecto-spinal tract suddenly becomes 



