8. W. Williston 303 



assumption, but there are evidences in its favor that give this idea some 

 weight. The strongly developed deltoid process shows attachments 

 for several muscles. One occupied the whole distal anterior face, as in- 

 dicated by an oblique line running from near the distal lower extremity 

 inward and upward. This was doubtless for the insertion of the supra- 

 coracoid muscle, the origin of which is shown by a strong tuberosity on 

 the upper part of the coraeoid, and whose tendon was guarded in part, 

 apparently, by a sesamoid bone found near the glenoid articulation. 

 On the distal convex border, near its upper extremity, there is a small 

 facet for muscular attachment, looking outward and forward in the 

 extended position of the arm. This may have been for the attachment 

 of the pectoralis, as Plieninger seems to believe, but of which I am very 

 doubtful. Certainly the pectoralis must have been a very weak muscle 

 to have terminated in so small a tendon, and the extensive surface 

 of the sternum calls for a large one. It would furthermore have acted 

 as a powerful muscle of inward rotatioi\, of which the joint was incapa- 

 ble. Lying in front of tlie arm and adjacent thereto, there are a num- 

 ber of long, thin, striated ossified tendons, with somewhat fimbriated 

 extremities, some of them eighty millimeters in length by four or five 

 in width. I am satisfied that the most of the space in front of the elbow 

 was filled during life by strong muscles, controlling the movement of 

 the arm and wrist, the anteiior brachial and carpal flexors, whose or- 

 igins were high up on the humerus. On the upper distal extremity of 

 tlie radius there is an articular surface extending backward, and, lying 

 near it in the specimen, there is a small sesamoid bone, doubtless be- 

 longing to a carpal flexor. Tlie pteroid bone has a rounded convex 

 articular surface on one side of its broad carpal extremity that evidently 

 fitted into a depression in tlie lateral carpal bone lying near it. The 

 joint seems to have permitted considerable enarthrodial movement, with 

 but little gliding motion; it clearly permitted considerable oscillation 

 of its free extremity in the plane of the wing. The distal extremity 

 reached nearly to the deltoid process in the ordinary flight position of 

 the wing. There certainly was not sufficient membrane in front of the 

 elbow to need such an elaborate structure for its support if the membrane 

 ceased at the shoulder. On the assumption that this bone is a reversed 

 thumb metacarpal, an altogether probable theor}^, one cannot conceive 

 how it could have assumed its present position, unless it had been re- 

 versed and brought toward the shoulder by the action of a membrane 

 that originally extended along the sides of the body over the outstretched 

 fingers like that of a bat. By the gradual development of the little 

 finger, as is shown, indeed, by the more elongated metacarpal of the 



