92 



largest of the Ruminants, and having the longest and most muscular 

 tongue in that order — is scarcely more than one-fourth the size, 



Immediately internal to the glenoid cavity is the large orifice of the 

 canal transmitting the third division of the fifth pair of nerves, the prin- 

 cipal branch of which endows the tongue with sensibility : this foramen 

 is rather less than that for the muscular nerve of the tongue*. 



Discovered in a tertiary stratum forming the bed of a river in Banda 

 Oriental, South America, and 



Presented by Charles Darivin, JEsg., F.M.S. 

 472. The lower jaw of the Mylodon Darwinii. 



The symphysis of this jaw, as in that of the My I. robustus, is completely 

 anchylosed, about four inches in length, and extended forwards to the 

 extremity of the jaw at a very slight angle with the inferior border of the 

 ramus ; it is of great breadth, smooth and gently concave internally, and 

 equally suggests the idea of its adaptation for the support and gliding 

 movements forwards and backwards of the free extremity of a long and 

 well-developed tongue. The exterior surface of the symphysis is cha- 

 racterised by the presence of two oval mammilloid processes, situated 

 on each side of the middle line, and about half-way between the anterior 

 and posterior margins of the symphysis. Nearly four inches behind the 

 anterior extremity of the above process is the large anterior opening of 

 the dental canal : it is five lines in diameter, situated about one-third of 

 the depth of the ramus of the jaw from the upper margin. The magni- 

 tude of this foramen, which gives passage to the nerve and artery of the 

 lower lip, indicates that this part was of large size ; and the two sym- 

 physial processes, which probably were subservient to the attachment of 

 large retractor muscles, denote the free and extensive motions of such a 

 lip as we have presumed to have existed from the size of the foramina 

 destined for the transmission of its nerves and nutrient organs. 



The angle of the jaw is produced backwards, and ends in an obtuse 



point slightly bent upwards : a foramen, one-third less than the anterior 



one, leads from near the commencement of the dental canal, to the outer 



* For the relation of so large a tongue to the probable habits of the Mylodon, see the Memoir on 

 the Myl. robustus, p. 15i. 



