38 ARBOREAL MAN 



described the ulnar head as normally present ; but Keith 

 has shown that it is absent in as many as 10 per cent, of 

 all examples dissected. Absence of the ulnar head is 

 more usual in the Gorilla; Hepburn regarded complete 

 absence as normal, but Keith has determined that it was 

 present, in some degree, in about 40 per cent, of all 

 individuals. 



In none of the Monkeys is an ulnar head present under 

 normal conditions, and the Lemurs are alike in this 

 respect (see Fig. 15). 



The ulnar head is absent in all other orders of Eutherian 

 Mammals, with the exception of at any rate some of 



-P.R/T J*, P ' RT - (1) 



-P.R.T.(2) 



-P.Q. -P.Q. 



FIG. 15. 



FIG. 15. DIAGRAM OF THE PRONATOR MUSCLES IN TYPICAL 



PRIMATES. 

 Lettering as before. 



FIG. 16. DIAGRAM OF THE PRONATOR MUSCLES IN A TREE SHREW 



(Tupaia ferruginea). 

 Lettering as in other diagrams. 



the Insectivora. In the Tree Shrews (e.g., Tupaia 

 ferruginea) there is (despite Kloster's assertion to the 

 contrary) a portion of the muscle deep to the median 

 nerve, and this portion arises from the upper extremity 

 of the ulna and from the internal collateral ligament 



