34 



ARBOBEAL 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 \mst, where it becomes 

 continuous with another set of fibres, which, arising from 

 the ulna, passes to the radial side of the ^^Tist and hand. 



— P.RT.(1) 



P.R.T.(2) 



P.M. 



-P.R.T.d) 

 P.R.T.(2) 



P.Q. 



Fig. 11. 



Fig. 12. 



Fig. 11. — Diagrammatic Figure of the Pronator Group of 



Muscles in CryptohrancJius. 



P.E.T. (1), Mammalian superficial head of pionatoiv radii teres. 

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

 Pronator quadratus. P.M., Prooator 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 

 lirevis. 



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. 



