402 THE INTER-MEDIATE PRIMATES 



extension of the reticular formation which passes between it and the superior 

 colliculus. The inferior colliculi are closely connected across the midline by 

 the commissure of the inferior colliculi. The superior coIHcuIar elevation 

 is much more massive than the inferior colhculus and is similarly situated, 

 being separated from the central gray matter surrounding the aqueduct of 

 Sylvius by a thin lamina derived from the dorsal extension of the reticular 

 formation. It is supported laterally by the same lateral extension of the 

 mesencephahc reticuhir iormation. Cephahcally it is limited by a thin exten- 

 sion of the lateral mesencephalic reticular formation. Mesially it rests against 

 the undiflerentiated dorsal gray matter and is connected with its fellow of the 

 opposite side by the commissure of the superior colliculus. 



The Red Nucleus 



The nucleus ruber is contained within the mesial mass of the mesence- 

 phalic reticular formation and receives at its caudal extremity the decussat- 

 ing superior cerebellar peduncle which forms an encapsulating mantle of 

 white libers about it, thus deiinitely outlining it from the surround- 

 ing matrix of the reticular formation. Although it is the outstanding feature 

 of the mesencephalon, it is relatively poorly developed in this form, extend- 

 ing upward even beyond the junction of the mesencephalon and diencephalon 

 into the substance of the latter division of the bram stem. 



The Central Gray Matter 



The central gray matter, as has been previously described, appears 

 in the higher levels of the cervical cord as a roughly cordiform structure 

 already separated from the ventral gray columns and providing a connection 

 with the laterally compressed dorsal horns. Continuing upward in this same 

 position, it gives origin to the dorsal extensions which form the nucleus of 

 the column of Goll, and at a somewhat higher level it presents the 



