MYOLOGY OF THE ORNITHORHYNCHUS. 151 



by latei'al flattening to be inserted tendinous into the ulna, along the 

 radial edge of that bone from scarcely beyond the elbow-joint half 

 way to the wrist (there being no coronoid process for its definite 

 insertion). 



Thus the two flexors of the forearm, ulnar and radial — inner and 

 outer — preserve ordinary relations in the forearm ; the biceps not 

 splitting below to have part of its insertion into the ulna, as in cer- 

 tain marsupials. There are only two other muscles that act upon the 

 forearm, viz. : the round pronator and short supinator ; for the square' 

 pronator is absent, and the long supinator, as usual among mammals, 

 is a humero-carpal muscle. The arrestation of this muscle on its way 

 to the carpus and its insertion into the styloid process of the radius, 

 is a teleological modification only found among the very highest 

 mammals. 



Pronator radii teres. — Although the forearm is fixed in semi-prona- 

 tion, this constant muscle is well developed. It is not, however, 

 superficial, and so determining the contour of the part, nor does it 

 arise first or highest up on the entocondyle, but it is deep-seated, and 

 overlaid in greatest part by the '^flexor" carpi radialis. It is a single 

 terete subfusiform belly, with origin from the entocondyle next below 

 the last named muscle, passing obliquely to be inserted into the mid- 

 dle third of the radius by a rather long, flat tendon, in relation, on its 

 radial aspect, with the tendons of biceps and brachialis anticus. Its 

 function is limited to steadying of the parts. 



Supinator brevis. — A deep-seated, triangular plane of moderate 

 size ; its outer, free border stretches in a straight line between the 

 tip of the ectocondyle and the middle of the radius, and the body of 

 the muscle fills the depression between these points. It has no ulnar 

 origin; but arises from the anterior border and tip of the ectocon- 

 dyle, and has definite, fleshy insertion iuto the upper half of the 

 radius — ending just in advance of a point opposite the insertion of 

 the pronator teres. It counteracts this last, but its action must be 

 very limited. 



c. Acting upon carpo-metacarpus, from humerus or forearm. 



The contour of the forearm is that of a flattened flask, broad above, 

 and rather suddenly contracting to a narrow neck towards the wrist. 

 Above, the fleshy bundles are widely sepai*ated, by the whole distance 

 between the tips of the expanded condyles of the humerus ; they are 

 thick and bulgmg, which may be said also of the muscles upon its 

 back. As usual, the aggregate bulk of the muscles upon the front is 

 greater than that of those upon the back ; but the latter are more uu- 

 mei'ous. The disposition of the muscles is simple, compared with 

 that of most higher unguiculates, and there are several notable ab- 

 sentees, as will be stated further on. 



COMMUNICATIONS ESSEX INSTITUTE, VOL. VI. 20 April, 1871. 



