OF THE SPINAL CORD 141 



any rate in animals ; in monkeys a section of these 

 tracts produces more paralysis than one involving 

 the crossed pyramidal. They appear to convey 

 impulses increasing muscular tone, so that when the 

 pyramidal fibres are damaged, as by a haemorrhage 

 in the internal capsule, muscular tone is increased 

 and a spastic hemiplegia results. There are, however, 

 other descending paths open to this class of impulses, 

 some of them crossing in the cord. 



ASCENDING TRACTS. The dorsal and ventral cere- 

 bellar tracts pass to the cerebellum, and are practically 

 uncrossed. They convey, amongst other things, the 

 so-called kinaesthetic sense, composed of sensations 

 derived from joints, muscles, and tendons, to the 

 cerebellum, and so keep it informed of the position 

 of every joint, and the state of contraction of every 

 muscle. 



The posterior columns (of Goll and Burdach) are 

 also uncrossed in the spinal cord, and convey tactile 

 sense, muscular sense, joint sense, and so-called 

 " tactile discrimination," by which we determine 

 whether two compass points are single or double ; 

 the sense (stereognosis) by which we recognize unseen 

 objects by the feel as on putting a hand into a 

 pocket containing coins, keys, a penknife, paper, 

 etc. also travels by this route. 



There is another sensory path composed of relays 

 of nerve-cells in the grey matter, with short axons 

 passing up to a slightly higher level either in or close 

 to the grey matter. For the most part impulses 

 travelling by this route cross the cord, usually about 

 six segments after entering. Heat, cold, and pain 



