MEGALONYX 15 



The condyle is a convexity, two inclics in transverse diameter, and about three- 

 fourths of an inch in its antero-posterior diameter; and anteriorly it slopes to the 

 bottom of the notch in advance. 



The latter is much broader than in Mijlodon ; but the coronoid process is nar- 

 rower, though relatively much broader and shorter than in the Ai. 



The angular process also is relatively less broad than in Mylodon, and is shorter 

 and deeper than in the Ai. It projects backward but not upward ; externally it 

 is convex and internally concave, and on both sides is strongly relieved by promi- 

 nent ridges for muscular attachment. 



The inferior dental canal commences at the base of the coronoid process, one inch 

 and a half behind the last molar alveolus, and it presents one of its foramina of exit 

 external to the position of the last molar just below the margin descending from 

 the coronoid process, and the other at the side of the symphysial ridge immediately 

 in advance of the first molar alveolus. 



Measurements of the lotver jaw. 



Inches. Liuee. 



Length from angular process . . . . . . . . .12 6 



Depth at condyle ........... 4 3 



Depth at coronoid process .......... G 



Depth at third molar alveolus ......... 3 7 



Depth at hiatus separating the anterior two molars ..... 4 



Dentition. — As in all the sloth tribe the teeth of Megalonyx are long, fangless 

 columns, of uniform diameter in the adult condition; are deeply excavated from 

 their bottom for the reception of a persistent dental pulp ; and are arranged in the 

 order of five molars upon each side in the upper jaw, and four molars upon each 

 side in the lower jaw. 



In Megalonyx as in the Unau, the anterior tooth of the series in both jaws is 

 placed considerably in advance of the others, and in general form and position 

 conveys the idea of its being a true canine tooth (Pis. I, III, IV, V, VI, Fig. 2). 



As previously stated, the upper jaw of the skull in the collection of Dr. Owen 

 contains all the teeth except the second on the left, and the last on the right side 

 (PI. III). The lower jaw accompanying the skull contains only the second and last 

 of the right side (PI. V). 



Of the upper molars in the specimen just mentioned the first on both sides, when 

 removed from its socket, is found to be perfect except in the loss of the thin edge of 

 the pulp cavity. This tooth is strongly curved, being convex anteriorly and ex- 

 ternally, and concave posteriorly and internally. Along the curve of the anterior 

 border, it is five inches in length. In transverse section (Pis. Ill, XVI, Fig. 1), 

 it is elliptical with an inner median bulge, which in a trifling degree extends more 

 anteriorly. The triturating surface is worn concave in a sloping manner towards 

 the edge posterior to the inner bulge of the tooth, and except in the latter position, 

 is surrounded by an elevated border composed of the less worn, harder dentinal 

 substance. At the anterior two-thirds of the outer margin of the triturating surface, 

 the cementum is worn away for a short depth. 



