OSTEOLOGY OF CARNIVOROUS DINOSAURS. 



105 



back on the lower surface of the bone. It articulates as shown in figure 62, with 

 metacarpal II, with a flattened facet on the internal side of the proximal end. 

 Metacarpal II, the most robust element in the foot of 

 Ceratosaurus, has widely expanded ends, with a somewhat 

 slender, rounded shaft. The distal end, viewed from the 

 front, looks downward and slightly outward, and is shal- 

 lowly grooved. On the front near the distal articidar end 

 there is a prominent depression or pit, in which a posterior 

 median projection of tlie proximal phalanx appears to rest 

 when the foot is strongly flexed. The upper articular end 

 is squarely truncated with a slightly rugose articular sur- 

 face. Except for being relatively shorter this bone re- 

 sembles the second metacarpal of Antrodemus. Metacarpal 

 III is the longest element of the metacarpus. The proxi- 

 mal end is widely expanded, and triangular in outline when 

 viewed from the end. The distal end is quadrangular in 

 outlme, grooved but rather shaJlowly so, with a pit on the Fio.ei.— left radius or ceeato- 

 anterior face near the distal extremity as in metacarpal II. twe-No''^^4735""u s^Vm^'^ 

 The distal articular end as in metacarpal II is slightly nat. size, viewed from the 

 oblique to the longer axis of the bone, and looks inward. ^'''^^' 

 The whole end is rounded antero-posteriorly much as in metacarpal II. Meta- 

 carpal IV is the smallest element of the metacarpus, and apparently is fast becom- 

 ing fmictionless. It has a weak articulation with 

 metacarpal III on the posterior external side of 

 the proximal end. The proximal end is consid- 

 erably expanded antero-posteriorly, but little so 

 transversely. On the inner side the bone is hol- 

 lowed out for articulation ^vith metacarpal II. 

 The distal end is little expanded, presenting a 

 rounded articular end without grooving. 



Metacarpals II and III form the main support 

 of the foot. 



Phalanges. — In the left fore foot the proximal 

 phalanges of digits II, III, and IV were found in 

 place, so that their position in the manus may 

 be considered absolutely determined. 



The fore foot of Ceratosaurus also differs from 

 other known Theropods in having the proximal 

 phalanges of digits two and three of about equal 

 length. Proximal phalanx of digit II is ex- 

 ceptionally short and stout. The jiroximal end is 

 especially expanded antero-posteriorl}^, the ex- 

 pansion being largely on the palmar side, so that 

 its diameter (29 mm.) is equal to the length of 

 the bone. This end is keeled to fit the groove of the metacarpal. The distal end 

 is grooved, dividing the end unequally, the outer articulating facet or condyle 



Fig. 62.— Left fore foot of Ceratosaurus 

 NASicOENis Marsh. No. 4735, U.S.N.M. 

 Ttpe. 1 NAT. SIZE. Front view, I, II, lU, 



AND IV, DIGITS ONE TO FOUR. SHOWN AS RE- 

 STORED ON MOUNTED SKELETON. 



