62 



BULLETIN" 110, UNITED STATES NATIONAL MUSEUM. 



articulation of the intermedium. The remaining proximal surface is smooth, though 

 sloping toward the outside of the foot. Metacarpal III is reduced, being the weakest 

 element of the metacarpus. Although present with hoth feet, it was detached in each 

 instance. The character of the surfaces appears to indicate, however, that in 

 position it has a weak articulation with metacarpal II on the postero-external angle, 

 as shown in figure 40. Unlike the other metacarpals the distal articular end is 

 not grooved, but is smoothly rounded (fig. 45, a). The posteriorly directed facets 

 are weakly developed, but are separated by a shallow groove, as in metacarpals 

 I and II. 



Phalanges. — The phalangial formula is 2, 3, 4. All of the digits, as shown in 

 figure 45, are terminated with latterly compressed, sharply pointed claws, the 



first being especially robust, 

 the third much reduced in 

 size. The proximal phalanx 

 of digit one is the longest of 

 the series. The proximal 

 articular surface is concave 

 supero-inferiorly, with a 

 strongly developed vertical 

 keel, which articulates with 

 the deep groove on the dis- 

 tal end of metacarpal I. This 

 keel, as shown in figure 45, 

 c, divides this articular end 

 into two unequal concave 

 surfaces, the larger one be- 

 ing toward the outer side of 

 the foot. It is inclined to the 

 vertical axis of the bone and 

 when articulated rotates the 

 distal end so that the ungual 

 phalanx is turned inward 

 from the vertical, as shown 

 in figure 40. The articular surface for the claw is broadly grooved, and this 

 surface extends well backward on the underside, thus throwing the- articulated 

 ungual downward at nearly a right angle to the longer axis of the first pha- 

 lanx. The lateral pits are comparatively shallow, the one on the external 

 side being the better defined. Viewed from above the shaft is quite evenly 

 rounded transversely, while the ventral surface presents a flattened aspect. The 

 ungual of digit 1 is especially robust, with a regularly curved and sharply pointed 

 extremity. Well-defined lateral grooves run back from the tip on both sides, but 

 as they approach the proximal end curve downward, passing into a broad, smooth 

 surface on the posterior ventral surface. The proximal articular surface is keeled 

 as shown in figure 45, i. The proximal phalanx of digit 2 is shorter than the second 

 of that toe. The proximal end of the former is expanded, especially in the vertical 

 direction. The proximal end as compared with the same phalanx of digit 1 is only 



Fig. 45. — Digits of the eight foke foot of Antrodemus valens Leidt. Cat. 

 No. 4734, U.S.N.M. J nat. size. Lateral view, a, proximal articular end 



OF THE PROXIMAL PHALANX OF DIGIT III; 6, PROXIMAL ARTICULAR END OF 

 UNGUAL OF DIGIT I; C, PROXIMAL ARTICULAR END OF PROXIMAL PHALANX OF THE 

 LEFT FOOT; C 2 , CARPALE TWO; d, DISTAL ARTICULAR END OF METACARPAL I; in, 



intermedium; I, II, III, digits one, two, and three. 



