486 



THE NERVOUS SYSTEM 



dorsal horns are thus almost cut off from the deeper portions of 

 grey matter. 



The ventral horns are both long and broad. They present 

 three noticeable promontories or processes a ventral (ventro- 

 medial), a medial (ventro-lateral), and a lateral. The lateral, 

 because of its special prominence, 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 ven- 

 tral, and a lateral group, together with a small intermedia-lateral, 

 which is partially or completely detached from the dorsal por- 

 tion of the lateral group. There is also a small disseminated 

 central group of nerve cells occupying the deeper portion of the 

 anterior horn. 



The nuclei of the segments included in the cervical enlarge- 

 ment contain the centers for the musculature and sensory reflexes 

 of the upper limbs. The partial control of the pupillary move- 

 ments 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 re- 



^^ gion. The larger 



size is due to an 

 increase in the 

 white matter of 

 the posterior and 

 lateral columns, 

 consequent upon 

 the acquisition of 

 new fibres which 

 enter the subja- 

 cent segments 

 from the nerves 

 supplying the up- 

 per extremities, 

 together with an 

 increased number of centrifugal fibres from the cerebrum which 

 are distributed to the grey matter of this region. 



The anterior columns are also much increased in size by the 



FIG. 381. TRANSECTION OF THE SPINAL CORD OF A CHILD, 



FOURTH CERVICAL SEGMENT. 



Weigert stain, x 7. 



