T)80 MONOGRAPHS OF NORTE AMERICAN RODENTIA. 



which the close apposition of the ulna and radius would indicate, the rela- 

 tions of (heir various articular surfaces arc the same as those in cases where 

 pronation and supination are perfect, and such movements are doubtless con- 

 siderable in extent. 



Mantis. — The carpals are nine in number, in two rows, four in the proximal 

 and five in the distal series. The first bone of the proximal series, on the 

 radial side, develops a large, flat, falcate process as long as the 1st meta- 

 carpal, against which it lies; this process supports the outer one of the two 

 large palmar tubercles at the radial side of the hand.* The second bone of 

 this series, lunare if not scapholunare, is also of great size, irregularly semi- 

 lunar in shape, with an oval convex facet, which forms most of the radio- 

 carpal articulation. The outer two bones are much smaller. In the distal 

 row, one of the five bones is probably an "os intermedium ''; this and three of 

 the others are extremely small; the remaining larger bone is somewhat 

 uncinate. 



There are five metacarpals, of which the 1st is much shorter than the rest, 

 and directed obliquely away from them; the others are approximately parallel ; 

 the ratio of their lengths is 3d, 4th, 2d, 5tli, the last shortest. There is the 

 normal number of phalanges — two in the pollex, three in each of the other 

 digits. 



Pelvis. — The sacral portion of the pelvis has already been described 

 with the vertebra?, The pelvis is rather long, narrow, and parallel-sided, about 

 two and a half inches long from apex of ilia to the opposite extremity. The 

 general axis of each innominate bone is straight. The ilia project about one- 

 fourth of their length in advance of the sacrum (which terminates opposite the 

 posterior border of the acetabula) ; their anterior prolongations embrace the 

 whole of the last lumbar vertebra. The ilia are narrow trihedral bones,curving 

 anteriorly outward, and somewhat clubbed at the extremity ; the edges are 

 all sharp, but the superior border is especially prominent; the outer surface 

 is concave; the other two faces of the bone are flatter, the internal being 

 roughened for the sacroiliac synchondrosis. The shaft of the bone is con- 

 stricted just above the acetabulum, though still markedly triangular in section. 

 The acetabula are deeply cupped, surrounded by a prominent rim, except 

 posteriorly, where the lip of the cup sinks into a deep notch. The ischial 



* In the Beaver, there is said to be a larj;e " accessory" carpal ossicle. It may be that the bono 

 hero described is the homologous ossicle of Haplodon, which, if substantiated, would furnish additional 

 evidence of affinity between this genus ;uul Castor. 



