OSTEOLOGY OF CAKXIV0K0T7S DINOSAURS. 55 



to represent one of the double ribs such as found bj- Lambe at the posterior end of 

 the cuirass in Gorgosaurus. 



A study of these rather meager materials, therefore, shows that in Antrodemus 

 some of the abdominal ribs of the cuirass were certainly composed of three and 

 probably four segments on each side of the median line, so that a complete section 

 across the abdomen would consist of either six or eight distinct ossifications, with 

 every probability of there being a single median bone connecting the two lateral 

 series, thus making either seven or nine in all (fig. 39). 



FORE LIMB AND FOOT. 



Plates 5-7, fig. 3. 



The fore limb of Antrodemus as compared with the hind limb is relatively 

 small, but the large size of the processes and the rough nature of their surfaces 

 imply a powerful musculature. The great size of the terminal phalanges and the 

 general structure of the foot indicate that it was used exclusively for seizing, holding, 

 and tearing and that it had long ago lost its functions as an organ of progression. 



Fig. 39.— Transverse section of abdominal basket of Antrodemus, showing a tentative determination of the seg- 

 menation of the abdominal ribs. about j nat. size. 



The hand is relatively of enormous size, being slightly longer that the humerus and 

 nearly one and one-half times as long as the forearm. In general it resembles the 

 foot of Ornitholestes, but the bones are more robust, and there is no trace with 

 either foot of metacarpal IV. 



The carpus is ossified, being made up of two transverse rows, but the precise 

 number of elements composing it yet remains to be determined. These are three 

 digits, which have the phalangial formula of 2, 3, and 4. Digit 1 is the heaviest 

 of the series, and digit 3 is somewhat reduced (fig. 40). 



In a previous article '■ I have given a detailed description of a forelimb and 

 foot of Antrodemus, at that time referred to Allosaurusfragilis, but m order to make 

 the present accoimt of the osteological structure of the genus complete it is here 

 repeated with some few omissions and emendations. 



The fore limb figured by Marsh in the Dinosaurs of North America,- plate 11, 

 figure 1, as being that of Allosaurusfragilis Marsh, is a composite drawing, and is 

 not representative of the genus Antrodemus {Allosaurus), but is largely that of 

 Ceratosaurus. 



' Proc. U. S. Nat. Mus., vol. 49. No. 2120, 1915, pp. 501-513. ' Sixteenth Ann. Rept. U. S. Geol. Survey, 1896, pt. 1. 



