38 THOMAS DWICTIT OK 



of the medius and annularis; the fourth from the uhiar side of the latter. The accounts 

 of these muscles in various chimpanzees show trifling differences in most cases. 



Pronator quadratus. Similar on both sides. It is in two layers which are only 

 partly separable. The more superficial begins as a tendon at the top of the ulnar origin 

 and expands as it passes downward and outward across the muscle. It gradually 

 becomes muscular, and having reached the outside of the radius, runs downward (hidden 

 by the flexor carpi radialis) to the ridge of the trapezium. It is about 7 mm. broad at 

 the end. The deeper, more transverse part of the muscle runs somewhat slanting 

 downward to the radius. A few fibers near the radial side go to the front of the capsule 

 of the wrist. 



This is an anomaly very rarely observed in man. I cannot find any record of it in 

 the chimpanzee. Macalister observed it in a Bengal tiger, though it is not normal in 

 the Felidae. It seems to show that animals of diverse groups have a tendency to similar 

 variations which are not determined by heredity.' I am not aware that the pronator 

 quadratus as above described is normal in any mammal. 



Palmar muscles of the thumb. Ahrhictor hrerls runs from the annular ligament 

 and sesamoid bone to the base of the first phalanx. Its tendon, reinforced by tlie flexor 

 brevis, passes into an expansion with a tendinous insertion into the second phalanx. 



Opponens poU'icts from the annular ligament more or less fused with the flexor 

 brevis. 



Adductor pollicis transversus from the fibrous aponeurosis which is stretched over 

 the fourth metacarpal. It arises directly from the distal part of the third metacarpal. 

 There is a slight interspace allowing it to be divided into a proximal and a distal part ; 

 both in the same plane. 



Adductor obllquus from the base of the third metacarpal to the usual insertion 

 and by a very small tendon to the second phalanx. 



Flexor brevis has no inner head. Hepbuin found a rudimentary one. 



Palmar muscles of the little finger. Practically as in man. 



The interossei are discussed after the other muscles of the fore-arm. 



Extensor communis. Not remarkable. Portion for index easily separable in the 

 lower third of the arm. The tendon for the little finger sends fibers to the fourth. 

 Wilder found no tendon to the little finger. 



Extensor minimi digit!. This supplies both the fourth and fifth fingers (as Hep- 

 burn describes for the orang-outang and Beddard for '' Sally " ). 



The action of the extensor tendons seems to be nearly limited to the first phalanges. 



' The sicnificance of annmalips. Ainer. ii.it., Feb.. ISO'). ■ Vvne. Host. .sue. iiat. hist., 1801. 



