186 



BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



nent and deep ligament pit excises a portion of the fulcra* ridge Just beneath 

 the large circular central canal. Bej'ond (distal to) the fulcral ridge the joint 

 face is divided into two portions, an inner and an outer, of which the latter is 

 somewhat broader than the former, by a narrow intermuscular ridge which does 

 not reach quite to the distal edge of the joint face. The proximal half of the 

 area beyond the fulcral ridge is raised into a broad platform nearly on a level 



with the summit of the fulcral ridge; the 

 distal half is rather deeply excavated. This 

 excavation is especially prominent on the 

 inner side, in the form of a right angled tri- 

 angle, of which the right angle is over and 

 just to the inner side of the middle of the 

 central canal, the hypotenuse opposite is 

 slightly convex, and the angle just inside the 

 middle of the distal border of the joint face 

 is produced in the form of a very narrow but 

 deep groove along the distal border of the 

 outer half of the joint face to the outer distal 

 corner. This fossa, very large and triangular 

 on the inner half of the joint face, but on the 

 outer half reduced to a narrow band along the 

 distal border, contains muscle fibers. On the 

 outer portion of the joint face beyond the ful- 

 cral ridge the excavation is not so deep. Here 

 it takes the form of a right-angled triangle, 

 of which the right angle, sharply rounded off, 

 lies at the distal outer corner of the joint face, 

 the two adjacent sides are about the same 

 length, and the hypothenuse, running from 

 above the central canal just beyond the mid- 

 dle to the outer end of the fulcral ridge, is 

 concave, but more or less indefinite. This 

 fossa, less deep than that on the inner side of 

 the joint face, lodges a large interarticular 

 ligament. On the outer side this articula- 

 tion resembles very closely that on the distal 

 end of the radial, but on the inner side the 

 dorsal ligament fossa is more broadly rounded, and the narrowly linear muscular 

 fossa running along the distal border of the joint face expands into a large tri- 

 angular fossa occupying almost the entire inner side beyond the fulcral ridge. 



The articulation between the first and second segments of P^ : This is a fairly 

 typical oblique muscular articulation. The fulcral ridge, which, as usual, is very 

 prominent, is nearly parallel to the longitudinal axis of the arm, but the distal 

 end is slightly nearer that axis than the proximal. Outside the fulcral ridge is 



229. — Lateral view of type specimen 

 op ptecilometea scalaeis. 



