1901.] AFFINITIES OF TTDENODON. 173 



upper half is moderately rounded, and from the head to a little 

 below the middle of the bone it steadily decreases in thickness, so 

 that at the middle the diameter is ouly about one-half that of the 

 head. In its lower third the bone becomes flattened out to give a 

 broad articulation to the radiale (ra.). The broad end of the bone 

 has a deep depression on both its upper and under sides. Its 

 articular surface looks downwards and slightly outwards. 



The ulna (nZ.) is very nearly twice as long as the radius, and 

 considerably longer than the humerus ; its great length being due 

 to the greatly developed olecranon process (ol.\cf. also Plate XVIII. 

 fig. 7). The upper half of the bone is very strongly developed, and 

 the olecranon extends about as far beyond the sigmoid articulation 

 as it does in such typical lowly mammals as the Wombat and the 

 Porcupine. The point of the olecranon is directed slightly out- 

 wards, but it is not dilated like that of the Monotremes. On the 

 outer side of the ulna a short prominent ridge is seen bordering 

 the sigmoid articulation. On the inner side the upper part of 

 the ulna is deeply excavated after the manner seen in that of 

 Echidna, but to a much greater extent, as the border of the bone 

 forms a much more prominent ridge. The lower half* of the ulna is 

 much flattened. Like the radius, the lower end is slightly expanded ; 

 while the articular surface looks slightly towards the radius. 



Carpus (Plate XVI.). 



In the skeleton of Udenodon gracilis the carpus is almost per- 

 fectly preserved, and the various bones composing it have scarcely 

 been at all disturbed in position. In the proximal row are four 

 bones — radiale (ra.) intermedium (/.), ulnare (im.), and pisiform 

 (pi.) ; in the distal row are five carpals ; while in the middle is a 

 single centrale (c). 



The radiale or scaphoid (ra.) is abroad and considerably flattened 

 bone which occupies the greater part of the articular end of the 

 radius. Its dorsal surface shows a considerable depression 

 towards its outer end. It articulates with the radius, with the 1st 

 carpale, the centrale and the intermedium. 



The intermedium or lunar (t.) lies between the end of the radius 

 and the ulna and ulnare. On the upper side it has a fairly large 

 surface, but on the under it is "apparent as a slender plate fitting 

 in between the radius and the ulnare. 



The ulnare or cuneiform (un.) is considerably shorter in its 

 transverse diameter than the radiale, but of much greater length 

 antero-posteriorly. It articulates with the ulna, the intermedium, 

 the 4th and 5th carpalia, the pisiform, and probably with the cen- 

 trale. Bordering the Bide by which it articulates with the ulna 

 there is a prominent little oblique ridge, and at the distal and 

 inner corner of the bone is a little rounded eminence. 



The pisiform (pi.) is a little bone which articulates with the 

 outer side of the ulnare, and curves outwards and upwards, form in;; 

 part of the articulation for the ulna. 



