Chapter XIV 



HVLOBATES HOOLOCK, THE GIBBON, ITS BRAIN 

 AND BEHAVIOR 



Its Position amons: the Primates; The Proantbropoid Stage; Measureirienis and 



Brain Indices; Surjace Appearance 0/ the Brain; Internal Structure oj the 



Brain Stem in Cross Section 



T 



"^HE gibbons are usually assigned to the group of the higher anthro- 

 poids, with the quahlication, however, that in this group they are 

 the most remote from man. In the general appearance of their 

 brain they ally themselves much more closely with the intermediate primates. 

 This, in combination with the fact that by their adaptive radiation they have 

 become equipped preeminently if not exchisively as tree dwellers, seems to 

 justify their inclusion with those intermediate forms already described. The 

 designation of them as "Hylobates" is intended to indicate how exquisitely 

 these "tree walkers" are specialized for arboreal habitat. Their lives are 

 passed in the trees, through whose branches they move with a swiftness and 

 ease similar to those of a bird. When on terra firma they pass over its surface 

 a little awkwardly, yet with much facility although compelled to balance 

 themselves by holding their long arms over their heads and hastening their 

 footsteps lest they fall. Once, however, their slender hands come in contact 

 with the branches of a tree, a really marvelous change appears in their pro- 

 gression. Their uncertain gait is immediately replaced by a locomotion which 

 has all the grace, the accuracy, the speed of a bird in flight. 



Appearance and Habits of the Gibbon 



The body and head of the gibbon are relatively small, little larger 

 indeed, than some of the smaller macaques. The animal's legs are relatively 

 short and it has no tail. The characteristic feature of the gibbon is the 



