93 



surface of the jaw, a little below and behind the last molar tooth : this 

 foramen presents the same size and relative position on both sides of the 

 jaw. 



The base of the coronoid process begins external and posterior to the 

 last grinder : the whole of the ascending ramus of the jaw beneath the 

 coronoid process is excavated on its inner side by a wide and deep con- 

 cavity, bounded below by a well-marked ridge, which extends obliquely 

 backwards from the posterior part of the alveolus of the last grinder to 

 the inferior margin of the ascending ramus, which is bent inwards before 

 it reaches the angle of the jaw. 



The large foramen or entry to the dental canal is situated in the in- 

 ternal concavity of the ascending ramus of the jaw, two inches behind the 

 last molar, three inches from the lower margin of the ramus, and nearly 

 five inches from the elevated angle of the jaw : it measures nine lines in 

 the vertical diameter, and its magnitude indicates the large size of the 

 vessels which were destined to supply the materials for the constant re- 

 newal of the dental substances, which from their texture must be sup- 

 posed to have been rapidly abraded. About an inch behind the dental 

 foramen a deep muscular groove, about two lines in breadth, is continued 

 downwards to the ridge which circumscribes the internal concavity of 

 this part of the jaw, and perforates the ridge, which thus arches over the 

 canal : this structure is present in both rami of the jaw. 



The mylo-hyoid ridge is distinctly marked about an inch and a half 

 below the alveolar margin. Other muscular ridges and irregular emi- 

 nences are present on the outer side of the base of the ascending ramus 

 and near the angle of the jaw. 



In the Mylodon Darwinii the rami of the lower jaw are relatively 

 longer than in the Mylodon robustus, especially anterior to the molar 

 series, where they become more contracted vertically, and converge to a 

 narrower and longer symphysis. The posterior angular process is rela- 

 tively shorter and more bent upwards. The molar teeth project further 

 from their sockets in the specimen compared than they do in the My- 

 lodon robustus. The anterior outlet of the dental canal is single, and it 

 is more in advance of the first alveolus. The symphysis is not only 



