Chapter XIII 



RECONSTRUCTION OF THE GRAY MATTER IN THE 

 BRAIN STEM OF PITHECUS RHESUS 



Y^ I ^HE reconstruction of this species follows the general lines already 

 I laid down in the preceding reconstructions. It is particularly valu- 

 H ^ able as showing the structures in their interrelation and contin- 

 uity, and thus furnishes a more realistic idea of the actual disposition of the 

 more important masses of gray matter in the brain stem. So far as possible, 

 the descriptions have been made almost exckisively objective, reserving the 

 space for comment on the signilicance of the structures for the chapters on 

 summaries and conclusions. 



The High Cervical Level of the Spinal Cord 



In the high cervical level of the spinal cord at which the reconstruction 

 of the gray matter in macacus begins, the ventral gray cohnnn is already 

 detached from the central gray cohimn by the decussating libers of the 

 pyramidal tract. In outline the ventral gray column is somewhat oval, 

 directed ventrodorsally and laterally. It occupies the normal position of 

 the ventral gray column in the spinal cord but is reduced in size. The 

 central gray matter is somewhat cordiform in shape, presenting a ventral 

 apex and a dorsal base from the lateral angles of which proceed the 

 laterally compressed cervices of the dorsal gray column. The substantia 

 gelatinosa trigemini is seated like a cap upon the dorsal extremity of the 

 dorsal gray column and is already beginning to show the lateral swing 

 occasioned by the appearance of the dorsal medullary nuclei and the opening 

 of the fourth ventricle. 



As the higher cervical segments pass into the lowermost levels of the 

 oblongata, the ventral gray column becomes increasingly interspersed with 



