30 FOSSIL MAMMALIA OF THE 



Below the condyle the hind border of the ascending ramus describes a deep curve to 

 the backwardly produced end of the inflected angle of the jaw. The lower border of 

 this inflected part is straight, and is not continued into that of the horizontal ramus with 

 the undulated contour shown in Spalacotherium, Phascolotherium, and AmpJiitherium. 

 The depth of the ramus gradually lessens to the horizontal sloping symphysis, as in 

 Amphitheriiwi. 



The first incisor {i i) of Ambhtherium soricinum is procumbent, and continues forward, 

 as it were, the gentle curve of the lower border of the symphysis ; it has a long, slightly 

 expanded, obtusely terminated crown, but this is the worn configuration of the fossil 

 tooth and may not have been exactly its condition in the recent subject. The crown of 

 the second incisor {i 2) is less than half the length of that of the first, but is almost as 

 broad ; it rises at a distance equal to its own basal breadth from the first. The third incisor 

 {i 3) is similar to the second, and rises closer thereto. The crown in each of these incisors 

 is hollowed on the hinder and inner surface, so that the apex is subrecurved, as in 

 Myrmecohius (PI. 1, fig. 24). After a longer interval comes the crown of a fourth small 

 incisor (^, 4). Near this rises vertically, with a slight backward curve, the crown of a 

 tooth which, by its length, represents the canine (c) ; it terminates more acutely than do 

 the incisors, and the crown is narrower in proportion to the height than in them. 



Behind the canine, with an interval like that before the canine, is the simple low conical 

 crown of a minute premolar (^1). In closer proximity rises that of the second premolar 

 (jij 2)- From the apex of the cone, which is near the forepart of this tooth, the hhid 

 border slopes or curves backward, swelling inwardly, and representing a hind basal 

 prolongation or talon. The third premolar [p 3) presents a like type of crown, with 

 marked gain of size. The fourth premolar {p 4) increases in height, but not in basal 

 breadth. Each premolar is implanted by two fangs. 



The series of true molars begins by teeth much inferior in size to ^ 4 and p 3 : they 

 have acquired, abruptly as it were, their characteristic shape and complexity of 

 crown (fig. 1, B, magn. 6 diam.). This consists of a long and slender main cone, with an 

 anterior (e) and a posterior («) well-marked cusp, the anterior being the larger, and on a 

 higher level. The intervening tract of the inner part of the crown represents there a low 

 cingulum, rising to, without being well defined from, the base of the principal cone (0) 

 which rises in great proportion from the outer part of the crown. In one of the molars, 

 the third (fig.l, b), the intervening part of the inner side of the crown forms a small low 

 prominence before inclining to blend with the main external cone. The molars increase 

 in size to the third ; then gain, perhaps, a little in basal breadth to the sixth ; which, 

 therefore, by the analogy of hinder decrease of size in the molars of Myrmecohius 

 Spalacotherium, I do not regard as the last. The traces in the fossil at the interval 

 between rn 6 and the coronoid process would be, I think, rightly interpreted as those of 

 a socket. 



The molars and the last premolar form a series uninterrupted by any ' diastema.' 



