202 THE SURGICAL PHYSIOLOGY 



that this tract carries down impulses that inhibit 

 any excess of muscular tone. The vestibulospinal 

 and other tracts pass down in the an tero -lateral 

 columns, from the region of the pons and medulla. 

 They are important paths for motor impulses, at 

 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 cerebellar tract 

 passes from the cells of Clarke's column of the same 

 side to the cerebellum. It conveys sensations 

 derived from muscles, joints, and tendons to the 

 cerebellum, and so keeps it informed of the posi- 

 tion of every joint and the state of contraction of 

 every muscle. 



The ventral cerebellar tract of Gowers is composite 

 in nature. Most of the fibres are crossed. Some pass 

 to the cerebellum, others to the mid-brain, and the 

 important spinothalamic tract conveys sensations 

 of heat, cold, and pain, and probably also tactile 

 sense, to the brain. 



The posterior columns (of GoU 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 ; 



