I (IS 



DR. 0. W. ANDKKWS OX T11K 



There are three milk-molars, the hinder two of which arc replaced by premolars in 

 the ordinary way, i.e., from beneath. 



The first and second milk-molars are hilophodont, each ridge consisting of a pair 

 of tubercles; in the second (m.m. 2) the cingulum forms a ridge at each end of the 

 tooth. Tht' third (m.m. 15) is trilophodont with an anterior and a posterior ridge of 

 the cingulum ; this tooth remains in use sometime after the first true molar has come 

 into wear, the last two milk-molars are replaced hy premolars, the anterior of which 

 consists of a large anterior cusp with a smaller one internal to it, and a talon of two 

 or three small tubercles. The posterior premolar (Fm. 4) is quadritubercular, the 

 cusps forming t wo crests. Hot h the premolars seem to he shed very soon, probably 

 because the development of the large posterior molars leads to a forward movement ot 

 t he series. 



The first and second true molars are trilophodont, the cingulum forming a small 

 talon. The last molar consists of three ridges and a large talon consisting of three 

 or four tuhercles. 



The molars are bunolophodont, each transverse crest consisting of a number ot 

 distinct tuhercles and being primarily divided into an inner and an outer half by a 

 longitudinal furrow more or less clearly defined. In the upper teeth the outer half is 

 the higher and is composed of two transversely placed tubercles, so closely united that 

 they are often difficult to distinguish, and when worn the division between them may 

 he completely obliterated. The inner half of the crest consist of a main tubercle to the 

 antero-external and postero-internal sides, a pair of accessory tubercles are usually 

 attached so that in wear the inner lobe gives a trefoil or V-shaped surface, the apex 

 of the V being turned to the inner side of the tooth. In the intermediate molars the 

 anterior accessory cusp of the anterior lobe is united with the anterior cingular 

 ridge, while the posterior accessory cusp of the hinder lobe is united with the talon 

 formed by the cingulum ; it is from a succession of such talons that in the later forms, 

 the additional transverse crests of the molars seem to have been developed. The 

 talon of the posterior molar consists of several cusps. 



Lower Teeth (figs. 8 and 9). — Of the three milk-molars the anterior one is a small 

 blunt single-cusped tooth; the second is bilophodont, each ridge consisting of two 

 i ubercles ; there is also a small cingular ridge in front and a much larger one posteriorly ; 

 the third is trilophodont with a cingulum anteriorly and posteriorly. 



The first premolar has a large anterior tubercle and tubercular talon ; the second is 

 hilophodont. 



The first true molar is trilophodont with a small ridge of the cingulum in front and 

 a much larger talon-like one behind. The last molar has four transverse ridges and 

 a talon. 



In the details of their structure the lower molars are like the upper ones reversed, that 

 is to say, the outer side of the lower teeth corresponds to the inner side of the upper. 

 Comparing Tetrabeloclon with ElepJias we find that, so far as the skull is concerned 



