Spinal Cord 27 



thoracic and upper cervical regions in man. In the rat cord 

 examined by the writer, this projection was evident only in 

 the last two cervical and the first thoracic segments (PI. V.). 



Fig 2. 



Diagram of transverse section of the spinal cord of the rabbit f 

 in the region of the cervical enlargement, after Winkler. According to 

 V. Lenhossek and to Linowiecki, the cortico-spinal tract includes the 

 area here assigned to the rubro-spinal tract and extends dorso-laterally 

 to the surface of the cord. It will be observed that the location of the 

 crossed cortico-spinal tract in the rabbit, unlike that in the rat, cor- 

 responds with that in man. 



The efferent cells receive their stimuli chiefly, if not 

 entirely, through correlation fibres which may come from 

 neighbouring or distant parts of the cord or may descend 

 from the brain. The most important descending tracts in 

 the white matter are shown in the diagram (Fig. 1). The 

 only one of these which can be observed in sections of the 

 normal spinal cord of the rat is the cortico-spinal or pyramidal 

 tract {fascicidiis c or tico- spinalis cruciatus sen lateralis),^ 

 which stands out on account of the very poor myelination 

 of its fibres. It may be seen forming the ventral or deep 

 portion of the dorsal funiculus (PI. \^), a position which differs 

 entirely from that occupied by the same tract in man, where 

 it lies in the dorsal part of the lateral funiculus. In man, 



^The direct or ventral cortico-spinal tract of man does not appear to 

 be represented in the rat (see p. 53). 



