254 



PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. 



posterior border is deeply concave transversely, being a continuation 

 posteriorly of the median depression of this end. The proximal 

 half of the external lateral surface is concave antero-posteriorly, 

 forming a depression which receives a rugose convex surface on the 

 internal lateral surface of Metacarpal III. The distal lateral sur- 

 faces are quite smooth. 



Metacarpal III is the longest and most robust element of the five. 

 Its proximal end is subtriangular in outline, being longer than wide. 

 The shaft is constricted and at its smallest part would be subcircular 

 in cross section. The distal end is expanded both antero-posteriorly 

 and transversely. Like Metacarpal II this end is convex antero- 

 posteriorly and concave transversely, although the median depres- 

 sion is not so pronounced as in Metacarpals I and II. The external 

 lateral surface of the proximal end is roughened and during the 

 life of the animal it probably had direct cartilaginous articulation 

 Avith Metacarpal IV. As mentioned above, the proximal end articu- 

 lates principally with the intermedium and slightly with carpale 

 three. 



Metacarpal IV is shorter and more slender than Metacarpal II, the 

 shaft being more rounded. Viewed from above, the proximal end is 

 subtriangular and has a smooth concave end which articulates closely 

 with the distal end of carpale four. The distal end is proportionately 

 less expanded than the preceding metarcarpals, and unlike them 

 shows no pronounced median depression except on the anterior border. 



Metacarpal V is the most slender of the series, although longer 

 than Metacarpal I. Seen from above the proximal end is triangular 

 and like Metacarpal IV has a smooth, transversely concave articular 

 surface for union with carpale five. On the internal lateral surface 

 near the proximal end is a shallow concave depression which articu- 

 lates with an outward projection on the ]X)stero-external angle of the 

 proximal end of Metacarpal IV, forming rather a weak union with 

 that digit. The shaft is constricted, especially antero-posteriorly, 

 which gives it a flattened aspect. The distal end is but little ex- 

 panded, being convex antero-posteriorly, without median depression. 



Measurements of metacarpals of Specimen, Cat. No. ^277, U.8.N.M. 



Metacarpals. 



Length 



Breadth of proximal end 

 Breadth of distal end 



mm. 

 40 

 38 

 25 



Phalanges. — The phalangial formula beginning with the first digit 

 is 2, 3, 3, 3, 2. 



The proximal phalanx of the first digit is short, with lateral and 

 dorsal surfaces quite evenly rounded and palmar surface flattened. 



