ANATOMY OF A MONODACTYLOUS FOETUS 403 



lower animals even where the ulna is of small importance in the 

 forearm. 



It is to be noted that although the two humeral heads of the 

 triceps can produce no movement, as they both arise and insert 

 on the humerus, yet they are both well developed muscle masses. 



MUSCLFS OF THE FOREARM 



There has been great disturbance of the muscles in the fore- 

 arm, due to the absence of the ulna and reduction of the hand, 

 but it is still possible to homologise some of them with those of 

 the normal type. The others however are difficult to define and 

 the homologies given for them are more in the nature of proba- 

 bilities than of definite facts. The extensors seem to be more 

 reduced and more atypical than the flexors. 



EXTENSORS 



Mostly members of the superficial group are here present as all 

 of the deep group with one exception are absent. There are four 

 muscles to consider on this surface. 



1. Brachioradialis muscle (figs. 9 and 10, B.) 



Origin. High on the lateral epicondylar ridge of the humerus. 



Insertion. A very short cylindrical muscle running across 

 the bend of elbow to insert on the shaft of the radius at about 

 its middle point, and just to the side of the insertion of the 

 lateral portion of the brachialis muscle. 



This muscle is probably the brachioradialis and its shortening 

 is not extreme, having been noted in other cases, while in one 

 of the anthropoids, the gibbon, its insertion is normally high up 

 on the shaft of the radius. 



2. Common superficial extensor mass (figs. 9 and 10, C.E.M.) 



Origin. Lower part of lateral epicondylar ridge and outer 

 surface of lateral epicondyle of the humerus. 



