TROGLODYTES NIGER, THE CHIAIPANZEE 585 



(.'hnractrnstic dI tlir h\ poulossal aiul \a^'al miile-i, this lf\fl of tlu' hrain 

 stem illustrates with what ph\ktic constaiiCN the two great mitlci of the 

 vestibular ineehanisiti niaki- tluir appearaiiee m a topographieal [iosition 

 eorres|)o[ulnig to that oeeupit-cl hy the uuelei of Goll and Burdaeh at the 

 lowx'r k'\ els ot the axis. 



It rs not possible Ironi this ligure to lucige ol the (Imiensions, and eonse- 

 (|uentl\ till' lunetional proniiiieiiee ol tlu' ^"estihlllar eomplex in tlu- ehiin- 

 paiizee. Tlu' appearaiKx- ol it m reeonstruet ion and its surlaee relief in the 

 lloor ol the tourth \i-iitriele indieate that this eom|)le\, while somewhat less 

 proiniiu'iit than in the striet l\ arboreal primates, is eonsidi'rabb moreeonsj^ic- 

 uous than in man or gorilla. This obserxation eoineides with 1 lu' motor 

 activities upon whieh thi' chimpanzet' dipends lor its great spc-c-d in elimbing 

 as well as getting about, either U|)on all lours or m its somewhat awkward 

 upright posture on the ground. Studies of the actions of the chimpanzee in 

 capti\"it\- reveal the high degree ol balancing specialization which the 

 animal j:)()ssesses m its man\ intricate and delicati' j^erformances. The 

 relati\ e lightness ol its body, as compared to man and thi- gorilla, permits of a 

 facility in climbing possessed b\ neitlu'r ol the other [jrimatcs nu'iitioncd. 

 The adaptation oi its ieit and arms to locomotion in the trees as well as upon 

 the ground calls lor special de\ c-lo]:)ments ol balancing, which, combined 

 with other necessities in this respect, undoubtedly account lor the well- 

 de\(.loped central nuchanism illustrated In the large size of the vestibular 

 comi)le\. 



Ventral to Deiters' nucleus is the now much r^'duced mass ol tin- sub- 

 stantia gelatinosa trigemini (NR) whose outt'r margin is in contact with 

 the ckseendmg trigeminal tract (Trd). The outer surlaee ol Deiters' nucleus 

 as well as the (k'scending trigeminal tract are co\ered by a massu'c bundle 

 ol libers constituting the rt'stilorm body ilCP). The intermediate and 

 postoluary sulci still bound the lateral iiiternu'diale eminence marking the 



