RECONSTRUCTION OF PITHECUS RHESUS 403 



condensations situated more laterally than the preceding, which extension 

 forms the nucleus of the cohmm of Burdach. At the point where the 

 nucleus of the column of Goll begins to increase in size, there appears a 

 narrow, tongue-shaped prolongation of the central gray matter, which 

 gradually approaches the dorsal surface and then, extending laterally, the 

 entire mass of the central gray matter is drawn dorsally and laterally 

 flattening out to form the floor of the fourth ventricle. In its ventral surface 

 lie embedded the dorsal nuclei of the ninth and tenth cranial nerves, and 

 close to the midline appears the nucleus of the twelfth cranial nerve. Separat- 

 ing the gray matter of the ventricular floor and the reticular formation, lie 

 the longitudinally coursing fiber bundles of the posterior fasciculus mesially, 

 the fasciculus solitarius laterally, together with the peripheral condensation 

 of fibers which circumferentially limits the reticular formation. In its lateral 

 portion are embedded first the nucleus of the column of Goll, arid then the 

 nucleus of the column of Burdach, which become separated from contact with 

 the central gray matter by the appearance of the nucleus of Deiters. 



In the cephalic portions of the myelencephalon and the metencephalon 

 appear small masses of gray matter connected with the ventral aspect of the 

 central gray matter, extending along the tegmental raphe. These form a 

 connected series of nuclei lying between the posterior longitudinal fasciculus, 

 the predorsal bundle and the mesial fillet. 



The central gray matter is in close contact with the vestibular and 

 cochlear complexes throughout their extent in the metencephalon. At 

 the upper limit of the triangular nucleus (Schwalbe) of the vestibular com- 

 plex, the lateral walls of the ventricle begin to approach each other and as 

 the upper extremity of the ventricle is reached, the floor, roof and lateral 

 walls rapidly draw together and the aqueduct of Sylvius appears. The gray 

 matter surrounding the aqueduct of Sylvius is relatively massive on all sides. 

 Ventrally the central gray matter is continued forward as a long, tongue- 



