3QO TRACING OF IMPULSES. 



of the auditory path above the pons, deafness chiefly on the 

 opposite side; and interruption of the gustatory path above the 

 medulla oblongata abolishes taste on the opposite (?) side. 



III. REFLEX PATHS. 



There is no visible limit to the number of reflex paths. Hence 

 no attempt will be made to give them completely, but a few ex- 

 amples of various kinds will be given which may assist the student 

 to trace others and be suggestive of their great multiplicity and 

 importance. Under certain conditions, unquestionably, the sen- 

 sory and motor paths that have been traced are but the afferent 

 and efferent limbs of reflex arcs. 



Reflex arcs are formed (i) by the sensory and motor fibers 

 of spinal nerves, associated in the gray matter of the cord; (2) 

 by the sensory and motor fibers of cerebral nerves, which are 

 connected in the brain; (3) by afferent spinal fibers connected 

 by the ascending fibers of the medial longitudinal bundle, with 

 efferent cerebral fibers; and (4) by afferent cerebral and efferent 

 spinal nerve fibers, the two being associated by the anterior 

 longitudinal bundle, the ponto-spinal tracts, the fasciculi proprii, 

 the spinal tract of the fifth nerve, the vestibulo : spinal tract, the 

 solitary tract, etc. 



(i) Spinal Reflexes (Figs. 112 and 113). In the simplest 

 spinal reflexes, the afferent fibers of the arc arborize about the 

 cell-bodies whose axones constitute the efferent fibers; the affer- 

 ent and efferent fibers are connected by one set of intervening 

 neurones in the next grade of reflex arc. Among these are the 

 skin and muscle reflexes, such as the plantar, the patellar, the 

 gluteal and the cremaster reflexes, the involuntary withdrawing 

 of a part from a source of irritation, etc. 



Coordinating and equilibrating reflex impulses traverse much 

 longer arcs. They are composed of the spinal ganglion neurones, 

 the external arcuate fibers (and probably the [posterior] cerebello- 

 spinal tract) in the afferent limb, and the descending anterior 

 cerebello-spinal tract and the anterior root neurones in the effer- 

 ent limb of the reflex arc. 



