RECONSTRUCTION OF MYCETES SENICULUS 241 



inferior colliculus and it is connected across tlie midline with its fellow of the 

 opposite side by the superior collicular commissure. 



The Nucleus Ruber 



In the reconstruction, the nucleus ruber in Mycetes senicukis appears as 

 a fairly well-diflerentiated and encapsulated mass of gray matter in the mesial 

 portion of the reticular formation. It receives at its caudal extremity the 

 decussating fillers of the superior cerebellar peduncle. These libers are con- 

 tinued about the nucleus, forming a capsule for it and many of them are 

 continued upward beyond the nucleus ruber into the subthalamic region. 

 The upper extremity of the nucleus ruber projects into the diencephalic 

 reticular formation and the nucleus in general seems to be located at a more 

 cephalic level than is the case in the human brain stem. 



The Central Gray Matter 



The reconstruction of the central gray matter as lirst observed in the 

 higher cervical level is somewhat cordiform in outline and is separated from 

 the ventral gray column. To its dorsolateral corners are attached the bases of 

 the dorsal gray columns. As the ventricular level is approached a narrow 

 prolongation of gray matter is seen to arise from its dorsal aspect and passing 

 along the dorsal median septum it divides into two tongue-shaped processes 

 which flare out on either side. This is the first indication of the opening of the 

 fourth ventricle. The central gray matter passes outward and backward, 

 gradually flattening into a narrow ribbon of gray matter lying under the 

 ependyma of the fourth ventricle. There the narrow strip of gray matter is 

 continued around the lateral boundaries of the ventricle, both in the inferior 

 and superior medullary velum so that the entire ventricular cavity is sur- 

 rounded by material derived from or continuous with the original central 

 gray matter. The gray matter of the floor of the fourth ventricle is relatively 



