THE FOKE LIMB AND FOOT. 



61 



THE RADIUS. 



The radius is slender when compared with the ulna. It is of moderate strength, however, 

 and somewhat expanded at either extremity. The shaft is subcircular in cross section, and 

 continues rather uniform throughout its entire length. The form is well shown in fig. 68. 



THE CARPUS. 



Nothing is known of the structure of the carpus in the Cera- 

 topsia, and I refrain from offering any suggestions as to what elements 

 entered into its construction or the probable 

 character of any of them. Future discoveries P 



will doubtless make known its structure. 



THE METACARPUS. 



This was composed of four well-developed 

 metacarpals, as shown in fig. 69. The metacar- 

 pals were much shorter than the metatarsals. 

 Metacarpal III was the largest of the series, but 

 was nearly equaled in size by II and IV, while 

 metacarpal I was smaller than the others. All the 

 metacarpals were functional. Their form is well 

 shown in fig. 69 and in PI. XVII. In all the 

 metacarpals the shafts were constricted, with the 

 extremities much expanded. 



THE PHALANGES. 



Fig. 67. — Anterior view of ulna 

 of Triceratops prorsus 

 Marsh, No. 4S42, U. S. Na- 

 tional Museum, in mounted 

 skeleton, o, Olecranon proc- 

 ess; r, surface for proximal 

 end of radius. One-eighth 

 natural size. After Marsh. 



Fig. 68. — Radius of Triceratops 

 serratus Marsh, No. 970 

 American Museum of Nat- 

 ural History, d, Distal 

 extremity; p, proximal ex- 

 tremity. One-eighth nat- 

 ural size. 



Nothing is definitely known of the number 

 or arrangement of phalanges in the manus of the 

 Ceratopsia. From the nature of the metacar- 

 pals, however, there can be no reasonable doubt 

 that the manus was mesaxonic in structure, and 

 that the phalanges of the third digit were larger 

 than those of the lateral digits, while it is quite possible, also, that the middle digit may have 

 borne one phalanx more than digits II and IV and perhaps two more than did the first digit, 



though these are mere conjectures 

 II i and have not as yet been con- 



firmed by direct observations. No 

 manus even fairly complete has as 

 yet been discovered. The pha- 

 langes of the proximal series are of 

 moderate length, with the longitu- 

 dinal diameter exceeding the trans- 

 verse. The intermediate phalanges 

 are short, the transverse diameter 

 exceeding the longitudinal. The 

 unguals are broad and depressed. 

 They are laterally expanded distally 

 and constricted proximally. They 

 exhibit a coarse cancellous struc- 

 ture, and during the life of the 

 animal were evidently incased in 

 The form and character of the various phalanges are 



Fig. 69. — Anterior view of metacarpals of Triceratops serratus, No. 970, American 

 Museum of Natural History. One-fourth natural size. Drawn by R. S. Lull. 



a horny substance resembling hoofs. 

 well shown in fig. 70. 



