THE SPINAL CORD 603 



tened, its transverse diameter (14 mm.) considerably exceeding its 

 anteroposterior. The major portion of the white matter is stilF con- 

 tained within its dorsal rather than its ventral portion, the gray com- 

 missure appearing to lie somewhat ventrad of the center. The dorsal 

 median septum dips inward for a much greater distance than does the 

 ventral median fissure. 



The dorsal columns are decidedly larger than the ventral, and a 

 distinct groove, the pa'ramedial sulcus, from which a fibrous septum 

 is continued inward, separates the dorsomedial from the dorsolateral 

 column. 



The dorsal gray horns are long, relatively slender, and more divergent 

 than in the lower levels. They do not reach the surface of the spinal 

 cord, but are connected therewith by the long, slender dorsal nerve 

 roots. The gray matter of the dorsal horns in this region is more or 

 less invaded by bundles of nerve fibers derived from the lateral and 

 dorsal columns; the tips of the dorsal horns are thus almost cut off 

 from the deeper portions of gray matter. 



The ventral horns are both long and broad. They present three 

 noticeable promontories or processes a medial (ventromedial), a ventral 

 (ventrolateral), and a lateral. The lateral, because of its special promi- 

 nence, is frequently called the lateral horn; it is one of the noticeable 

 characteristics of the cervical region. 



Each of these processes contains a corresponding cell group; hence 

 we distinguish in the cervical enlargement a mesial, a ventral., and a 

 lateral group, together with a small intermediolateral, which is partially 

 or completely detached from the dorsal portion of the lateral group. 

 There is also a small disseminated central group of nerve cells occupying 

 the deeper portion of the ventral horn. 



The nuclei of the segments included in the cervical enlargement 

 contain the centers for the musculature and sensory reflexes of the upper 

 limbs. The partial control of the pupillary movements in the eye is 

 also located in the lowermost segments of this region. 



In the upper half of the cervical region a transection of the spinal 

 cord, except for its larger size, resembles very closely that of the thoracic 

 region. The larger size is due to an increase in the white matter of 

 the dorsal and lateral columns, consequent upon the acquisition of 

 new fibers which enter the subjacent segments from the nerves sup- 

 plying the upper extremities, together with an increased number of 

 centrifugal fibers from the cerebrum which are distributed to the gray 

 matter of this region. 



