COMPOSITION AND CENTRAL CONNECTIONS OF SPINAL NERVES 853 



are said not to enter the inferior peduncle but to pass with the ventral spinocere- 

 bellar fasciculus. The cerebellar reflex arc is supposed to be completed by the fibers 

 of the superior peduncle which pass from the cerebellum to the red nucleus of the 

 mid-brain where some of their terminals and collaterals form synapses with neurons 

 whose axons descend to the spinal cord in the rubrospinal fasciculus. The terminal 

 and collaterals of this fasciculus end either directly or indirectly about the motor 

 cells in the anterior column. 



The ventral spinocerebellar fasciculus, since most of its fibers pass to the cere- 

 bellum, is also supposed to be concerned in the conduction of unconscious muscle 

 sense. The location of its cells of origin is uncertain. They are probably in or near 

 the dorsal nucleus of the same and the opposite side; various other locations are 

 given, the dorsal column, the intermediate zone of the gray matter and the central 

 portion of the anterior column. The neurons of the first order whose central fibers 

 enter the fasciculus cuneatus from the dorsal roots send collaterals and terminals 

 to form synapses with these cells. The fibers which come from the opposite gray 

 columns cross some in the white and some in the gray commissure and pass with 

 fibers from the same side through the lateral funiculus to the marginal region 

 ventral to the dorsal spinocerebellar fasciculus. The fasciculus begins about the 

 level of the third lumbar nerve and continues upward on the lateral surface of 

 the spinal cord and medulla oblongata until it passes under cover of the external 

 arcuate fibers. It passes just dorsal to the olive and above this joins the lateral 

 edge of the lateral lemniscus along which it runs, ventral to the roots of the trigem- 

 inal nerve, almost to the level of the superior colliculus, it then crosses over the 

 superior peduncle, turns abruptly backward along its medial border, enters the 

 cerebellum with it and ends in the vermis of the same and the opposite side. Some 

 of its fibers are said to join the dorsal spinocerebellar fasciculus in the medulla 

 oblongata and enter the cerebellum through the inferior peduncle. A number of 

 fibers are said to continue upward in the dorsolateral part of the tegmentum as 

 far as the superior colliculus and a few pass to the thalamus. They probably form 

 part of the sensory or higher reflex path. 



The posterior root fibers conducting impulses of pain and temperature probably 

 terminate in the posterior column or the intermediate region of the gray matter 

 soon after they enter the spinal cord. The neurons of the second order are supposed 

 to pass through the anterior commissure to the superficial antero-lateral fasciculus 

 (tract of Gowers) and pass upward in that portion of it known as the lateral spino- 

 thalamic fasciculus. This fasciculus lies along the medial side of the ventral spino- 

 cerebellar fasciculus. It is stated by some authors that the pain fibers pass upward 

 in the antero-lateral ground bundles. In some of the lower mammals this pathway 

 carries the pain fibers upward by a series of neurons some of which cross to the 

 opposite side, so that in part there is a double path. In man, however, the lateral 

 spinot .alamic fasciculus is probably the most important pathway. On reaching the 

 meduJa these fibers continue upward through the formatio reticularis in the neigh- 

 borhood of the median fillet to the thalamus, probably its ventro-lateral region. 

 \Yhether higher neurons convey the pain impulses to the cortex through the internal 

 capsule is uncertain. The pathway is probably more complex and Head is of the 

 opinion that our sensations of pain are essentially thalamic. The pain and temper- 

 ature pathways in the lateral spinothalamic fasciculus are not so closely inter- 

 mingled but that one can be destroyed without injury to the other. 



Ransom suggests that the non-medullated fibers of the posterior roots, which 

 turn into Lissauer's tract and ascend or descend for short distances not exceeding 

 one or two segments and finally end in the substantia gelatinosa, are in part at 

 least pain fibers and that the fasciculus of Lissauer and the substantia gelatinosa 

 represent part of the mechanism for reflexes associated with pain conduction and 

 reception while the fibers to the higher centers pass up in the spinothalamic tract. 





