175 



extremity of the large posterior one is curved forwards, in one of its divi- 

 sions, from which the cement has been detached : the equidistant parallel 

 transverse ridges are remarkably well defined. 



From the tertiary deposits of Missouri. Purchased. 



716. The right ramus of the lower jaw of the Mastodon giganteus, showing 

 the socket of the antepenultimate molar and the penultimate and last 

 molars in situ : the former presents three principal transverse ridges, 

 each divided into two mammillary processes, and an anterior and pos- 

 terior talon ; the last molar presents five transverse ridges with an 

 anterior talon and posterior tubercle ; three of the ridges have emerged 

 from the socket : the dental canal commences by a depression on the 

 inner side of the neck of the condyle, and becomes wider and deeper as 

 it descends obliquely forwards to its bifurcation in the substance of the 

 jaw, six inches behind the posterior alveolus : its principal anterior outlet 

 is on the outside of the jaw about two inches below the anterior alveolus ; 

 a smaller continuation of the canal may be observed in the fractured 

 surface of the symphysis, indicating the position of the socket of the 

 lower incisor, which is lost in the female Mastodon, as she advances to 

 maturity. 



The lower jaw of the Mastodon giganteus differs from that of the Mast, 

 elephantoides and of the Elephant in the smaller antero-posterior extent 

 of the ascending ramus and the greater height of the condyle, in the 

 more marked angle between the horizontal and ascending ramus, in the 

 straighter contour and much greater depth of the posterior margin lead- 

 ing from the condyle to the angle, in the more compressed form, the 

 greater length and the less convex sides of the horizontal ramus, in its 

 less degree of breadth inferiorly, in the greater vertical extent of the sym- 

 physis, and in the angle formed between it and the upper margin of the 

 jaw anterior to the molar teeth, which margin does not descend to join 

 the symphysis. 



From the tertiary deposits of Ohio. Purchased. 



717- A portion of the right ramus of the lower jaw of the Mastodon giganteus , 

 showing the sockets of the penultimate and last molar tooth. 



From the tertiary deposits of Ohio. Purchased. 



