1066 ON A SUPPOSED NEW SPECIES OF NOTOTHERIUM, 



Distinguished from /V. mitchelli, Ow., by the size and structure 

 of the premolar and position of the inlet of the dental canal ; from 

 N. inermis, Ow., by the develoi)ment of the tusks and consequent 

 retrocession of the symi)hysial curve ; from D. victorice, Ow., by 

 the position of the inlet of the dental canal and by the gradual 

 enlargement of the molars serially. 



Description of a left recently adult mandible (No. 5489) 

 m^ coming into use. The symphysial slope makes with the 

 base of the jaw an open angle of 20°; the upper surface of the 

 symphysis ascends gently from the incisive outlet to the level of 

 the premolar, then descends withamoi-e rapid curve to the vertical 

 of the mid-valley of m^ ; above its posterior margin is a small 

 subcircular depression for insertion of ligament. The convexity 

 of the inner mandibular wall is at this age feeble, even beneath 

 m" ; the concavity of the lower part of the wall is consequently 

 shallow and broad, and confined to the part above the angle, which 

 is feebly reflected and very obtuse. The diastema is equal in 

 length to that of the two anterior true molars ; its edge surmount- 

 ing the rapidly sloping surface of the symphysis sharp, and it 

 descends with a gentle curve and inclination to the incisive outlet. 

 The alveolar line makes with the diastema a graceful sigmoid 

 curve ; on the outer side anteriorly the mandibular wall descends 

 sheer from the diastemal edge ; on the vertical of d^-m^ it becomes 

 convex and it increases in convexity as far as the root of the 

 coronoid process, which, in this stage of growth, springs upwards 

 opposite to the fore lobe of m^ ; the fore edge of the coronoid 

 plate, so far as it is preserved, inclines forward ; the postmolar 

 platform is as yet incompletely formed ; its inner angle is obtuse 

 and shax'p-edged ; its outer end is confluent with a low broad 

 buttress rising with a backward slope upon the side of the ascend- 

 ing ramus ; this convex surface ends abruptly in the fore edge of 

 the inlet of the dental canal, which at this period is distant from 

 the postmolar angle by a space equal to the length of m' ; the 

 direction of the inlet is caudo-dorsad ; the anterior orifice of the 

 canal is just anterior to the forefang of the premolar. 



