Chapter VI 



RECONSTRUCTION OF THE GRAY MATTER IN THE 

 BRAIN STEM OF CALLITHRIX JACCHUS 



Dorsal Sensory Nuclei 



THE nucleus of Goll first becomes apparent in the reconstruction as a 

 small sessile projection connected with the dorsal surface of the cen- 

 tral gray column. It rapidly extends dorsally as a narrow prolonga- 

 tion of the central gray column and presents at its extremity a laterally flaring 

 termination. It is situated close to the midline and separated from the dorsal 

 median septum by a thin lamina of libers. At a somewhat higher level a small 

 collection of gray matter appears in the dorsal portion of the reticular forma- 

 tion. This consists of the nucleus of Burdach which, like the sensory 

 nucleus of Goll, rapidly expands as it extends cephalad. Attached laterally 

 to the main nuclear mass and presenting the characteristic arboreal form 

 seen in the lemur is the external nucleus of Burdach (Blumenau). The effect 

 of the opening of the fourth ventricle is already apparent in the divergent 

 arrangement of the overhanging dorsal masses of the nuclei of Goll and Bur- 

 dach. As these nuclei take their origin from the central gray column and the 

 reticular formation mesial to the point of confluence between the dorsal gray 

 column of the spinal cord and the central gray column, the former is slowly 

 and gradually shifted laterally, and its expanded cap, the substantia gelat- 

 inosa Rolandi, under the influence of the opening ventricle, shows a similar 

 lateral inclination. The transition from the Rolandic to the trigeminal gelat- 

 inosa occurs without sharp line of demarcation except that the trigeminal 

 gelatinosa is constantly increasing in size as it ascends. In outline this struc- 

 ture presents a serrated surface, the indentations being occupied by the 



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