SIMIA SATYRl'S. THE ORANG-OUTANG 503 



of the decussation (Pyx) tlu- \ fiitroiiu-sial sulcus is dcdccted to the left 

 and the \entral gray column (Ven) is almost entirely separated from 

 the central gray matter (Ccn). The latter structure has mowd into a 

 more caudal position m the early stages oi" that migration w hieh e\entuates 

 m lorming the llo(ir oi the lourth \entricle. In the most ventral portion of 

 the sectifMi some hbers of the pyramid ( Py ) still keep tluir position 

 characteristic ol the oblongata. I'he dorsal sensory field is broad and (.'Xijan- 

 sive. It contains the usual (.■lements: the column of Goll (CG) representing 

 the leg, the column of Burdach (CB) representing the upper e\tremit\-, 

 and tlu' descending trigeminal tract (Trd) representing the sensor\- terri- 

 tories ol the lace. A small detached nuclear mass in the column of GoII 

 represents the nucleus ol Goll. No such miclcai- structure is present in the 

 column of Burdach. The nucleus of Rolando (NR), on the other hand, is 

 ol considerable size, although distinctl\ less in dimensions than is true of the 

 lower or intermediate primates. The central gray matter (Cen) extends 

 almost transversely across the section from a small central canal outward 

 to the nuck'Lisol Rolando. Immediately \entral to it are some of the collected 

 bundles of the pyramid (XPy) in their course extending into the spinal 

 cord. On the periphery of the section are the two spinocerebellar tracts 

 (Fie, Gow), and \ eiitronu'sial to the latter is the spin()-oli\ar\- bundle 

 of Helweg I H el ). The Deiterso-spinal tracts ( DT ) lie ventral to the \ cntral 

 gray column (Ven), while the rubrospinal ( Rst ) and spinothalamic iS|:)t ) 

 bundles occupy their usual positions m the intermediate mcdLillar\' substance. 

 The mterpretation to be gi\en to this level with reference to its major 

 tLinctional elements concerns tlu' marked increase in the Nolume of the 

 p\ ramidal decussation, indicative of accessions in the voluntary control 

 which the animal possesses over tlu' muscles, and the large size of the 

 column of Burdach as com])ared with the similar sensory columns providing 

 inllux Irom the lower extremitx and Irom tlu- head. The disparity which 



