68 Field Columbian Museum — Geology, Vol. II. 



angles to the dorso-ventral plane, for the radius ; a second shorter 

 and less thick one for the ulna joins this at a small angle ; beyond 

 this, the thinned ulnar expansion is lost in the specimen, but doubt- 

 less had two facets for the third and fourth bones of the epipodial 

 row. On the ventral surface of the bone above, proximad to the 

 middle, there is a large, stout rugosity for muscular attachment. The 

 very strong muscle attached to it doubtless arose from the ventral 

 surface of the coracoid. On the ulnar border of the bone, at its 

 middle, there is a more pronounced, though smaller rugosity, for 

 muscular attachment. The peculiar tooth-like projections on the 

 outer posterior angle of the coracoid described in Dolichorhynchops 

 osborni probably indicates the origin of the muscle inserted into 

 this* rugosity. It may be called the ulnar rugosity. On the 

 radial border, a little beyond its middle, there is a smaller and less 

 strong rugosity Avhich may be called the radial. The origin of the 

 muscle inserted here probably was on the lower part of the scapula. 

 The dorsal surface of the shaft is smooth, without muscular roughen- 

 ing beyond the tuberosity. The distal portion of the bone is much 

 expanded, thickest toward the radial side, and moderately thinned at 

 the distal outer margin. 



Of the four muscular rugosities, which doubtless furnished 

 attachment for nearly all of the muscles controlling the arm, those of 

 the tuberosity are of course the largest, though the large roughening 

 on the ventral side may have been for the insertion of more powerful 

 muscles, which were of course much more effective from the greater 

 mechanical advantage under which they acted. The movement here, 

 though strong, could not have been through a great range. The 

 smallest of all, and placed much further away from the fulcrum is 

 the radial. The great convexity of the head indicates considerable 

 freedom of rotation. The glenoid surface in the articulated skeleton 

 of Dolichorhynchops looks nearly directly outward. The obliquity at 

 which the head of the humerus is placed as regards the horizontal 

 plane, indicates that the natural resting position of the flipper was at 

 about forty-five degrees downward, but I doubt whether the extrem- 

 ities of the paddles could have been raised much, if any, above a 

 horizontal position. It is further certain that the flippers could not 

 have been brought back against the side of the body. The posterior 

 angle of the coracoid, projecting as it does beyond the plane of the 

 glenoid surface, certainly prevented any great backward movement 

 of the humerus. It seems also evident from this position of the cor- 

 acoid, that the paddle was not so pedunculated as restorations usually 

 have them, but that the humerus was largely or entirely hidden in 



