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PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



with caution in the diagnosis of human lesions. Head and Thomp- 

 son, in the paper previously referred to, conclude, upon the basis of 

 extensive clinical studies, that in man all the fibers of cutaneous 

 sense cross in the cord except those mediating tactile discrimination. 

 As stated above, these latter pass upward in the posterior funiculi 

 together with some of the fibers of muscle sense, and do not cross 



Fig. 79. — Diagram of the afferent nerve-fibers and their course in the spinal cord: a, Specific 

 receptor for painful impulses; h, specific receptor for heat impulses; c, specific receptor for cold 

 impulses; d, specific receptor for tactile impulses; e, specific receptor for impulses of passive 

 position and tactile discrimination; /, specific receptor for non-sensory afferent impulses; 1, 

 sensory fibers of the second order for pain, heat, and cold; 2, sensory fibers of the second order 

 for touch; 3, sensory fibers of the second order for passive position and tactile discrimination; 

 4, long fibers (uncrossed) in the posterior column of the cord; 5, spinocerebellar tracts (lateral 

 columns) for non-sensory afferent impulses (from Thompson, slightly modified). 



until after they reach the medulla. These authors in studying the 

 sensory paths in the spinal cord make a distinction, in the first place, 

 between cutaneous sensibility and deep sensibility. By the latter 

 term they designate the senses of pressure, of pain, and of position 

 resident in the muscles, tendons, and other parts beneath the skin. 

 Cutaneous sensibility they divide further into epicritic sensibility 



