214 INITIATIVE IN EVOLUTION 



aspect of the humerus for a variable distance. In the baboon and 

 others it goes to be inserted into the inner inter -muscular septum 

 and the internal condyle of the humerus, in the orang to the con- 

 dyle, and in the gibbon to the centre of the shaft. As to origin it 

 proceeds from the insertion of the latissimus dorsi, but in the gorilla 

 from the coracoid process of the scapula and from two portions of 

 the pectoralis minor, and is finally attached to the inter -muscular 

 septum between the brachialis anticus and the triceps ; in the 

 chimpanzee it divides into an anterior and posterior portion, the 

 former being attached to the inner condyle, the latter to the 

 middle and inner head of the triceps ; in the orang it divides 

 similarly, but in one particular example it had an anterior 

 thin portion attached by a slender tendon to the coracoid 

 process of the scapula and a posterior portion arose from the 

 latissimus dorsi ; in the white-handed gibbon it arose from the 

 function of tendons from the latissimus dorsi and teres major 

 and was inserted into the fascia between the tendon of the biceps 

 and the brachialis anticus. 



Such a divergence as this within the strict limits of an 

 anthropoid muscle, concerned in the various forms of climbing 

 action of these apes, can only suggest an origin from a 

 divergent set of functions and small details in their respective 

 modes of climbing. 



Hand and Foot of Man. 



Both the hand and foot of man supply a small muscle for 

 consideration in the present connection of habit with formation of 

 new structure. If man be regarded as of simian origin there are 

 not as many entirely new muscles in his equipment as would be 

 expected from his departure from the habits of simian ancestors, 

 though many muscles are found to be altered in size and shifted 

 from the ancestral positions. But the human hand presents one 

 suggestive example of a little muscle not found in any other animal, 

 the special small extensor of the thumb, arising from the interosseous 

 membrane between the radius and ulna, and from the radius, being 

 segmented off from the extensor of the metacarpal of the thumb, and 

 it accompanies this muscle and tendon to be inserted into the first 

 phalanx of the thumb, and is peculiar to man. It can be easily 

 seen at the radial border of the well-known " snuff-box " which 

 is produced by it when it is fully extended. This is of course a 

 muscle of small importance to the functions of the hand, and its 

 appearance in man can only be supposed to be a subordinate detail 

 easily derived from the greater extensor by reason of the more 



