616 THE FUNCTION OF THE SPINAL CORD 



of the spinal cord. It is to be noted, however, that these defects differ in different 

 animals in accordance with the state of development of these tracts. They are 

 most apparent in the apes and man and less evident in lower animals, in which 

 the pyramidal system is always rather incomplete. In the latter, other motor 

 paths serve to bring the spinal nuclei into unison with the higher centers. This 

 is also true of the dog, because the division of the pyramids causes merely a par- 

 tial paralysis of the muscles, and still permits the stimulktion of the cerebral 

 cortex to evoke certain movements.^ Clearly, therefore, the results obtained by 

 experiments upon lower animals cannot be directly applied to man. 



(6) The anterior tectospinal bundle, or Held's bundle, lies just beside the entrance 

 to the anterior median fissure. It has its origin in the superior quadrigeminal 

 colliculus and descends through the dorsal tegmented decussation, midbrain, pons 

 and upper half of the medulla to a place between the pyramidal decussation and 

 the isolated head of the anterior columna. It is concerned with the production of 

 the ocular and pupillary reflexes, of ^ which circuits it forms the central division. 



(c) The rubrospinal or prepyramidal tract, also called Monakow's bundle. It 

 is triangular in outline and is situated anterior to the crossed pyramidal tract. 

 Its fibers may be traced from the red nucleus, a group of cells situated in the midbrain 

 anterior to the nucleus of the third nerve. Shortly after their origin they cross the 

 midline of the body and descend through the pons, medulla and cord to the level of 

 the lumbar region, where they arborize around the cells of the posterior extent of the 

 anterior horn. This tract appears to be an adjunct of the pyramidal system, 

 because the red nucleus is connected with the cerebrum and cerebellum. 



(d) The vestibulospinal tract is composed of descending fibers which are scattered 

 through the anterior funiculus in the immediate vicinity of the root fibers. They 

 arise in the lateral vestibular nucleus (Deiters') in the medulla and terminate in 

 the spinal gray matter. It may be inferred, therefore, that this tract constitutes 

 an important transmitting system between the cerebellum and the cord, being 

 directly concerned with the adjustment of the musculature to sensory stimuli from 

 the semicircular canals. 



(e) The olivospinal tract or bundle of Helweg. It is a small tract and is situated 

 near the surface of the cord just lateral to the anterior roots. Its fibers are said to 

 arise in the thalamus and to extend through the inferior olive of the medulla as far 

 as the lower cervical region. 



(J) The comma tract of Schultze is situated in the posterior funiculus of the 

 cervical and upper thoracic regions. It occupies the anterior realm of the column 

 of Burdach, and appears to be formed by the descending branches of the posterior 

 root fibers. Many of the latter divide into ascending and descending branches and 

 thus connect afferently with different levels of the cord. For this reason, they 

 cannot be regarded as forming true descending tracts. A similar origin is ascribed 

 to Lissauer's bundle which embraces the tip of the posterior horn, as well as to the 

 oval field of Flechsig and the median triangle of Gombault and Philippe. 



(g) The septomarginal bundle is oval in shape and borders upon the posterior 

 median fissure. It contains short fibers, but has been said to embrace also certain 

 fibers from the midbrain. 



2. Ascending Tracts. — (a) The posterior tracts occupy the fasciculi gracilis and 

 cuneatus, and are formed almost wholly by the axones of the cells situated in the 

 ganglia of the spinal roots. Several of them also arise from different segments of 

 the spinal gray matter. The former are characterized as exogenous and the latter 

 as endogenous; moreover, while some of these fibers terminate at different levels 

 of the gray matter, others extend through the entire length of these columns and 

 eventually end in the nucleus gracilis and nucleus cuneatus of the medulla. The 

 former, very clearly, are spinal associative in their function, while the latter belong 

 to the projection system and form a part of the afferent side of this cerebral con- 

 ducting path. During their course through the cord, these fibers remain on the side 



iRothmann, Zeitschr. f. klin. Med., xlviii, and Schafer, Quart. Jour, of Exp. 

 Physiol., iii, 1910, 355. 



