AFFERENT, OR SENSORY PATHS. 383 



sensation are conducted through these paths is unknown. Under 

 certain conditions, perhaps, they may carry all varieties, (i) The 

 antero-lateral fasciculus proprius and formatio reticularis contain 

 ascending axones which may convey sensory impulses from the 

 gray matter of the cord, received from the posterior roots of the 

 spinal nerves, and from terminal nuclei in medulla and pons 

 which receive the common sensory fibers of cerebral nerves, up- 

 ward to the thalamus of the opposite side. The course from the 

 thalamus is by way of the cortical fillet. (2) Again, impulses 

 may leave the formatio reticularis in the pons and run through the 

 brachium pontis cerebelli, by way of axones from the nuclei pon- 

 tis, to the cortex of the cerebellum; and then continue by the or- 

 dinary course through the brachium conjunctivum to the red 

 nucleus and thalamus. 



Destruction of any of the above sensory paths causes diminu- 

 tion or loss of the especial variety of impulse which travels that 

 path. Destruction of the posterior white columns produces 

 loss of muscular sensations and gives rise to ataxia. Interrup- 

 tion of Gowers's tract (spino-thalamic and ascending anterior 

 cerebello-spinal tracts) abolishes pain and temperature sensations 

 while touch is not much affected. 



2. Special Sensations. 



Impulses producing the sensations of smell, sight, hearing 

 and taste are carried from the respective organs of sense to the 

 brain by the following nerves: The olfactory; the optic; the 

 auditory; and the glossopharyngeal and intermediate nerves. 



Olfactory Path (Figs. 109 and 21). Impulses of smell orig- 

 inate in the upper third of the nasal mucous membrane. They 

 run through the olfactory nerves to the second layer in the bulb, 

 where they are transferred to the dendrites of the mitral and brush 

 cells. By the axones of these cells they are carried backward 

 through the olfactory tract and striae to the cerebral hemisphere. 

 The medial stria conducts them to the parolfactory area (Brocae), 

 the triangle, the gyrus subcallosus and anterior end of the gyrus 

 cinguli, whence, through the cingulum, the fornix and uncinate 

 fasciculus they may reach the cortical area of smell in the uncus 



