34 ARBOREAL MAN 



arises from the ulna. This sheet, which passes from the 

 ulna to the radius, is oblique in direction -above, but 

 more transverse nearer to the wrist, where it becomes 

 continuous with another set of fibres, which, arising from 

 the ulna, passes to the radial side of the wrist and hand. 



P.R.T. (1) SL .__ 



P.R.T.<2) 

 P.R.T. (2) 



-P.Q. 



-P.M. 



FIG. 11. FIG. 12. 



FIG. 11. DIAGRAMMATIC FIGURE OF THE PRONATOR GROUP OF 

 MUSCLES IN Cryptobranchus. 



P.R.T. (1), Mammalian superficial head of pronator radii teres. 

 P.R.T. (2), Deep Mammalian head of same muscle. P.Q.> 

 Pronator quadratus. P.M., Pronator manus. 



FIG. 12. DIAGRAM OF THE PRONATOR MUSCLES IN MAN. 



P.R.T. (1), Superficial, humeral, head of pronator radii teres. 

 P.R.T. (2), Deep, ulnar, head of same muscle. P.Q., Pro- 

 nator quadratus. S.L., Supinator longus. S.B., Supinator 

 brevis. 



There is therefore in this generalized animal a more 

 or less continuous pronator sheet, the proximal part of 

 which is superficial, and passes from humerus to radius, 

 where it blends with an intermediate part. This second 

 part is deeper, and passes from ulna to radius, and, in its 

 turn, blends with a distal part which passes from the 

 ulna to the radial side of the third segment of the limb. 

 From this unspecialized condition, advance takes place, 



