APTEEODON MACfiOGNATHUS, 227 



condyle by a deep notch and is slightly inflected. The coronoid process is incomplete. 

 The dental canal {d.f^ opens low down near the ventral border. On the outer face of 

 the mandible there are four or five foramina, of which the most anterior is beneath the 

 alveolus of pm. 1, the next beneath the middle of pm. 2, the third and fourth beaeath 

 the front and hinder roots respectively of pm. 3. The third molar is represented by its 

 alveolus only. The second consists of a high anterior portion and a large talon with a 

 blunt cutting-edge. The anterior portion consists of a large posterior cusp with a much 

 smaller one closely united to its antero-internal side, the two together forming a very 

 blunt and imperfect blade ; in Pterodon and JHycenodon the antero-interual cusp is 

 enlarged and secant, and with the posterior cusp forms the powerful cutting-blade of 

 the carnassials. There is no trace of a postero-internal cusp. The first molar is much 

 smaller than m. 2 ; it is greatly worn, particularly on its antero-external face. The 

 anterior half of the tooth is composed of a small antero-internal cusp (paracone) and a 

 larger main posterior cusp (protocone). The talon consists of an outer cusp and a lower 

 inner ridge apparently continuous with the cingulum. 



The fourth premolar is much larger than m.l; it is composed of a large stout main 

 cusp and a small talon. The second and third premolars are simple compressed cones, 

 each borne on a pair of relatively large roots. In both premolars and molars the 

 cingulum is well marked. Pm. 1 is represented by its alveolus only; it seems to have 

 been a one-rooted tooth squeezed outwards between the hinder edge of the canine in 

 front and pm. 2 behind. The canine is relatively large, and there are three incisors 

 so crowded together that one, probably i. 2, is displaced so as to lie above and behind 

 the other two. 



The dimensions (in centimetres) of this specimen are : — 



Total length of the jaw ... 22 



Depth of ramus at binder end of symphysi.s . . . 3'2 



„ „ beneath m. 3 . . . . 3-2 



Length of sympbysis . . 5-8 



Width of condyle 2-3 



Distance between hinder border of the alveolus of m. 3 and 



the posterior angle of the condyle 10'2 



Antero-posterior diameter of canine 2 



The dimensions (in centimetres) of the cheek-teeth are : — 



Length. Width. 



m. 3 (alveolus) 1'6 



TO. 2 . . . . . . . 1-6 -9 



m. 1 . . 1-2 -7 



pm. 4 . . . .... 1-7 1 



jpm. 3 . . . 1-4 -9 



pm. 2 . ... . . . . . 1'2 "7 



M. 8880. Plaster cast of above specimen. Made in the British Museum. 



C. 8815. Posterior portion of right ramus of mandible with m. 1-3 in perfect preservation (text- 

 fig. 73). The description given above of the second molar in specimen C. 8982 applies 

 equally to m. 2 and m. 3 in this mandible. It can, however, be seen that the cingulum 



2g2 



