OSTEOLOGY OF CARNIVOROUS DINOSAURS. 



73 



axis of the bone. On the fibular side two heavy blunt processes extend outward 

 from the main body of the astragalus to articulate with the calcaneum. The 

 upper, which is also the heavier of the two processes, shows an articular surface on 

 the lower half of its posterior side for articulation with the calcaneum. The upper 

 half apparently extends free, and thus with the upper articular surface of the 

 calcaneum forms a cup-like socket for the distal end of the fibula. The lower 

 process, which is separated from the upper by a notch (fig. 50, B), embraces a portion 

 of the ventral surface of the articulated calcaneum. 



The distal surface is subconvex antero-posteriorly, having a broad shallow 

 depression near the middle, which makes it concave transversely. 



Measurements of Astragalae of Antrodemus valens Leidy. 



No. 7336, 

 U.S.N.M. 



No. 4734, 

 U.S.N.M. 



Greatest height about 



Greatest transverse diameter 



Greatest antero-posterior diameter 



mm. 

 125 

 155 



mm. 

 115+ 

 132+ 

 90 



Metatarsus. — The metatarsus of Antrodemus consists of four bones of which 

 three are large, and support strong functional toes, and one, the first, is in the 

 process of reduction. 



The first digit or hallux was first recognized and described by Osborn 1 as 

 follows : 



Of greatest interest is the first digit or hallux, not before described. Proximally [fig. 51] its meta- 

 tarsal fits in a shallow groove of the upper portion (on the postero-external side) of the large metatarsal 

 II. The shaft is entirely interrupted or composed of cartilage in the> middle portion. Distally it is 

 fitted to the rounded posterior shaft of metetarsal II, demonstrating that this digit was directed inwards 

 like the small hallux of Apteryx. [In metatarsal II of both specimens Nos. 4734 and 8423, U.S.N.M., 

 the point of contact with the lower portion of metatarsal I is indicated by a flattened rugose area]. It 

 possesses, however, a complete and functional phalanx and claw, which undoubtedly were of service 

 in grasping. 



Specimen No. 4734, U.S.N.M., has the lower half of the first metatarsal of the 

 right side preserved, but in none of the specimens in the United States National 

 Museum collections is the upper half of this bone present. The proximal portion 

 of metatarsal I is well shown in figure 2, plate 7, reproduced from a photograph 

 kindly furnished me by Mr. Walter Granger, of the American Museum of Natural 

 History. 



Metatarsals II, III, and IV are elongate elements, the median one being the 

 longest of the three. Their proxmal ends are closely apposed to one another, as 

 shown in figure 51. Metatarsals II and IV are subequal in length, the former hav- 

 ing a straight shaft that throws the distal end outward from the median metatarsal. 

 All three of these metatarsals have cupped proximal ends. The face of metatarsal 

 II which is applied to metatarsal III is plane, while the opposite side is angularly 

 convex with a notch on the posterior outer margin for the reception of the proximal 



i Osborn, H. F. Bull. Amer. Mus. Nat. History, vol. 12, 1899, p. 163. 



