72 BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



Measurements of calcaneum of Antrodemus valens Leidi/. No. 4734, U.S.N. M. 



mm. 



Greatest length (antero-posterior) ''S 



Greatest height ^'^ 



Greatest breadth "^O 



Astragalus (.4s.).— In specimen No. 4734, U.S.N.M., the left astragalus is 

 firmly conjoined, if not actually coossified, with the tibia. A detached left astrag- 

 alus. No. 7336, U.S.N.M., from "Quarry No. 1,"' Canon City, Colorado, which 

 clearly shows all of the principal features of this element, is the basis for the de- 

 tailed description given below. 



Viewed from the front, the astragalus consists of a heavy rectangular lower 

 portion from which rises 



on its outer half a wide, -r-^n^ j4 



thin ascending process. /Mi'"'*^'^fcs5!SB»,,_ 



At the base it is slightly /Af'',i Xf"^^^^ 



more than half as wide // >^-- { ^ .'^^^A'' W 



as the lower portion /r7~"^ ^^i"- y''f^^'^^^m\ 



from which it springs. / -v - j^h^.^^'^" .^^_^/ '^ 



In outline this process is C. ,,^^«^Ri^ — ^"^""^^fe^ 

 angular, narrowing ^"^^-isi^ -»<^ 



rapidly toward the top. 



The anterior face is set £ ^^r-^ 



back from the heavier y:£f f^ /^!!'kk 



articular portion below m' '/'L 



and is further defined by • ^/'''f Wl MP 



a wide groove traversing ^ — ^—^\, "mH' /'^ 



its base from side to side. / ^ 4 ' ' ViV^^^^^ { 



Thelimitedextentof this \ \ ^^"' ~^Wi 



process in Antrodemus, [ , \ ' |L 



as contrasted with the I „„,, -^eiMMlmW t^ M"^" if~M 



Upper Cretaceous thero- ^^^^^^^^^J ^.^^-■. A^i^^^ ^^ 



pods, where it reaches ^'si^x\_^:j^ss^>^ ^^-o^S/^ 



its maximum develop- Fk. 50.— left astragalus of antrodemus valeksLeidy. No. 7336, U.S.N.M. } NAT. 

 ment and the Triassic ^'^^' ^' anterior view; B, dorsal view; C, -external view. 0». articular 



' . . SURFACE FOR CALCANEUM. 



theropods, where it is 



entirely absent, shows a progressive development of this process during successive 



geological periods. 



The main lower portion of the astragalus at about its center on the anterior 

 face is traversed by a shallow transverse groove, which deepens toward the inner 

 margin, and which turns downward slightly toward the external border when it ends 

 at the base of a deep notch. 



Viewed from above the surface on which the tibia rests is broadly concave 

 antero-posteriorly on the inner half, but on the outer half rapidly narrows becoming 

 V-shaped. At the base of the ascending process on the posterior side is a large 

 circular depression in the bone that at first glance gives the impression of being a 

 foramen. The inner end is heavy and obliquely truncated to the longer transverse 



