Chapter XV 



RECONSTRUCTION OF THE GRA\' MATTER IN THE 

 BRAIN STEM OF HYLOBATES HOOLOCK 



T 



"^HE reconstruction of the gray matter of the brain stem in Hylo- 

 bates hoolock begins at the caudal extremity of the inferior olivary 

 nucleus. The higher levels of the spinal cord are not represented in 

 the model and the ventral gray cokimns have ah-eady merged with the 

 reticular formation. 



The Dorsal Medullary Nuclei 



The nucleus of GoII, as first represented in the reconstruction, is already 

 of considerable size. It is roughly quadrilateral in shape with a broad base 

 which is confluent with the central gray matter. A large dorsal portion shows 

 some tendency towards that lateral swing which characterizes these nuclei 

 in the various brain stems ah-cady studied. 



The nucleus of Burdach arises slightly more cephalad than the nucleus 

 of GoH, in fact, at about the same level as that in which the inferior ohvary 

 nucleus appears. Its origin is represented by a thickening at the point of 

 junction between the nucleus of Goli and the central gray matter. The 

 nucleus rapidly increases in size, expanding laterally and, at its periphery, 

 somewhat ventrally, thus showing the same tendency towards the lateral 

 swing evidenced by all of these dorsal nuclear structures. It soon reaches its 

 maximum size and continues upward with httle change. At the level of the 

 lower thud of the fourth ventricle it begins to diminish and rapidly comes to 

 an end. 



Directly ventral to the nucleus of Burdach is the substantia gelatinosa 

 trigemini. This nucleus, as in other primates, has ah-eady reached a position 

 widely removed from the midline. It is oval in outHne with its long axis 



