624 THE FUNCTION OF THE SPINAL CORD 



(a) Higher or Lower Segments of the Cord. These are also reflex in character, 

 but involve the spinal gray matter and anterior roots of segments situated above 

 or below the point of their entrance. These segments are reached over the fibers 

 of the ground bundles or by way of the terminals and collaterals of the fibers of 

 the posterior columns. In the latter case, they are not relayed, because many of 

 the fibers of the posterior roots divide inside the cord into an upper and a lower 

 branch, the former eventually arborizing at a higher and the latter at a lower level 

 than their point of bifurcation. The connection between the terminals of this 

 afferent fiber and the anterior gray matter is effected in either case in the manner 

 just described. 



(b) Higher Centers in the Cerebellum and Cerebrum. The cerebellar impulses 

 are concerned with the muscle-sense and the coordination of muscular movements. 

 They are transferred from the posterior root to posterior cells and subsequently 

 to the cerebellar tracts in the lateral funiculus and the cerebellum. Some of these 

 are no doubt transferred directly to efferent channels, while others pass from this 

 organ to the cerebrum, where they may either enter consciousness or remain sub- 

 conscious. They then seek the efferent tracts by way of the motor areas. The 

 cerebral impulses leave the fibers of the posterior roots and enter either the pos- 

 terior tracts or those of the lateral funiculus. Inasmuch as no separate tract is 

 set aside for them by means of which they could reach the cerebrum directly, 

 they are relayed in the medulla and basal ganglia to secondary bundles of fibers. 

 These impulses serve conscious and subconscious reactions. In the first instance, 

 they enter consciousness as sensations of touch, pain and temperature. 



Nothing further need be said regarding the afferent impulses of 

 touch, pain and temperature, when concerned with reflex action. 

 Their course has been mapped out above under the headings of A 

 and B, a. Much controversy, however, has arisen as to their course 

 when they enter consciousness, and give rise to their respective sen- 

 sations which are then followed by voluntary reactions. This con- 

 troversy finds its origin in the diversity of the symptoms following 

 lesions of the posterior and lateral fasciculi. Thus, it has been ob- 

 served that the posterior tracts may be divided in lower animals 

 without destroying the sense of touch. Cases have also been recorded 

 of persons with extensive lesions of the same columns whose sense of 

 touch was not seriously impaired. But this evidence does not prove 

 that the tactile impulses do not enter the posterior tracts at all, but 

 merely suggests that two paths are open to them, namely, the long 

 projection fibers of the posterior funiculus and the short fibers of the 

 lateral funiculus. Thus, if the former fibers are destroyed, these im- 

 pulses are still able to gain the cerebrum by way of the latter. This 

 view, however, is not fully in accord with the results of experiments 

 upon lower animals, but is in agreement with the symptoms presented 

 by persons suffering from certain affections of the spinal cord. While 

 this matter cannot be definitely decided at the present time, it appears 

 that these differences are chiefly dependent upon the fact that the 

 spinal paths vary somewhat even among the mammals. 



If we confine ourselves to man, we may draw the conclusion 

 that the impulses of touch and pressure are transmitted under normal 

 conditions to the posterior tracts of the same side, but may be trans- 

 ferred in the upper cord to the opposite anterolateral columns. Head 



