HUMAN ANATOMY. 



The most conspicuous object within the tegmentum in the superior half of 

 the mid-brain is a large round reticulated field on each side of the median raphe, 

 which marks the position of the red nucleus (nucleus ruber). This body, also 

 called the nucleus tegmenti, is of an irregular ovoid form (Fig. 963) and of a reddish 

 tint when seen in sections of the fresh brain. Its lower limit corresponds with the level 

 of the lower margin of the superior colliculus, whilst its upper pole extends into the 

 subthalamic region. Its diameter increases towards the upper end and its long axis 

 converges as it ascends, so that the upper enlarged portions of the two nuclei lie 

 close to the mid-line and nearer each other than do the lower poles. Each nucleus 

 consists of a complex of gray matter and nerve-fibres. The latter preponderate 

 below, where the red nucleus receives the fibres of the superior cerebellar peduncle, 

 and are much less numerous above, since many fibres come to an end around the 

 rubral cells. These elements are very variable in shape and size (.020. -060 mm.), 

 but are most often irregularly triangular or stellate. The red nuclei constitute not 



FIG. 963. 



Optic fibres joining 

 superior colliculus 



Opttc 



thalamus 



Part of median 

 yeniculate nucleus 



Median 



kreniculate bodj 



Root-fibres of_ 

 third nerve 



Emerging fibres of 

 oculomotor nerve 



Inter- 

 peduncular 



space Red 

 nucleus 



Lateral geniculate body 

 Stratum intermedium 



Crusta of cerebral peduncle 

 Substantia nigra 



Transverse section of mid-brain at level O (Fig. 919), passing through superior colliculus and gen iculate bodies; 

 red nucleus, and nuclei and root-fibres of oculomotor nerve. Weigert-Pal staining. X 3- Preparation by Professor 

 Spiller. 



only important stations in the path connecting the cerebellum and spinal cord, but 

 also probably contribute links in chains uniting the cerebral cortex and the internal 

 nuclei with the cord. Whilst some of the constituents of the superior cerebellar 

 peduncle pass around the red nucleus and continue as cerebcllo-ihalamic fibres uninter- 

 ruptedly to the optic thalamus, the majority of the fibres of this arm end around the 

 cells of the nucleus. Of these many give off axones that proceed brainward as rubro- 

 thalamic fibres ; others emerge from the ventro-medial surface of the nucleus, cross 

 the mid-line (decussation of Forel) and bend downward as the rubro-spinal tract. 

 The latter descends within the tegmentum of the mid-brain and pons, traverses the 

 medulla and finally enters the lateral column of the cord as one of the important but 

 uncertainly defined descending tracts. Other fibres enter the red nucleus on its 

 lateral aspect and establish connections between the cerebral cortex (Dejerine), and 

 probably also the corpus striatum (Edinger), and the nucleus. From the cells of 

 the latter tin- path is continued by fibres which join the rubro-spinal tract, and in 

 this manner establish an indirect motor path that supplements the cortico-spinal 

 tracts identified with the pyramidal. 



