120 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XIV. 



somewhat obliquely with its small anterior cusp slightly internal to its 

 high triangular posterior blade. Posteriorly it stands closely against the 

 first molar and, although its principal cusp is higher than any of the 

 molars, it is functionally a member of the molar series and fairly well 

 separated from the anterior teeth as in diprotodonts generally. It is 

 slightly thickened posteriorly but has no internal cusps although the 

 cingulum is well-developed. Of its two roots, the anterior one beneath 

 the small antero-internal cusp is the longer and heavier. 



UPPER MOLARS. 



Description. The first and second molars are essentially alike in 

 structure and size, the first being only very slightly longer relative to its 

 width. They are quadrate and have four principal cusps, two inner and 

 two outer, i. e., paracone, metacone, protocone, and hypocone. 1 At the 

 inner base of the metacone is a small but high and very distinct inter- 

 mediate conule which in worn teeth is sometimes obliterated. In lateral 

 view, the paracone and metacone appear as nearly equilateral triangles 

 rising from the cingulum. The angle between these two cusps is more 

 acute in the first molar than in the second and both cusps of the first are 

 slightly higher than those of the second. The protocone is well developed 

 and more thickened but is somewhat lower than the outer cusps. At its 

 antero-internal base it is distinctly bulging. A distinct internal cingulum 

 bounds its base and extends to the anterior base of the hypocone. The 

 hypocone is about half as high as the protocone and its apex scarcely 

 reaches the height of the intermediate conule, so it is much the smallest 

 of the four principal cusps. Protocone and paracone are connected 

 anteriorly by a commissure which forms the front boundary of the deep 

 central depression of the tooth. A low commissure connects the proto- 

 cone and the hypocone and near the middle of this is a slight ridge some- 

 what imperfectly connecting the posterior base of the protocone with 

 the intermediate conule. Between the hypocone and the intermediate 

 conule there is an open channel to the back of the tooth. 



The third upper molar is subtriangular and the hypocone is prac- 

 tically undeveloped, although a very slight shelf exists between and 

 slightly posterior to the intermediate conule and the protocone. The 

 first, second, and third molars have three strong roots each and these 

 are situated respectively beneath the protocone, paracone, and meta- 

 cone. The external cingulum in all these teeth is well-marked, but shows 

 no differentiation into styles. The fourth molar is very small, scarcely 



1 These terms and others are used without reference to homologies to designate 

 the cusps to which they have been commonly applied in connection with the Cope- 

 Osborn tritubercular theory. 



