80 ON THE EXTINCT MAMMALIA OF 



its complete character; the teeth of the permanent set being forty-four in number, 

 arranged in nearlj' unbroken series in both jaws. The genus besides presents many 

 well marked peculiarities in the construction and arrangement of the teeth. The 

 formula of the permanent dentition is as follows : 



3—3 _ 1 — 1 4—4 3—3 



Incisors , canines , premolars — , molars — =44. 



4—4 1—1 3—3 3—3 



The molar teeth, seven in the upper jaw and six in the lower jaw on each side, 

 form unbroken rows. When the jaws are closed the cusps of the lower molar teeth 

 are included in the angular interspaces of those above. The premolars above and 

 below have their outer faces nearly on the same plane ; the lower true molars are 

 situated considerably within the position of the outer portion of the upper true 

 molars. 



The true molars correspond in number, general proportions of size, relative posi- 

 tion, and plan of construction, with those of existing ruminants. Among the latter 

 they approach most nearly those of the Deer family, and, as in this, are inserted into 

 the jaws by distinct fangs alone, when the crowns occupy their functional position. 



The crowns of the upper true molars are composed, in the usual manner among 

 ruminants, of four crescentoid demi-conoidal lobes. They are nearly square, the 

 transverse and antero-posterior diameters being nearly equal, but their length is much 

 less. They resemble those of the Deer, but are more spread transversely, more 

 square, and of less proportionate length ; the interlobular spaces are more open and 

 shallow; the faces of all the lobes are more sloping from the perpendicular, and the 

 inner lobes are uncomplicated with accessory folds. The outer lobes anteriorly, and 

 consequently where the lobes conjoin in each tooth, form buttress-like columns more 

 prominent than in the Deer. These columns are laterally compressed towards the 

 masticating border, but expand towards the bottom of the crown. In the last molar 

 a similar buttress-like column, but less well developed, occupies the back part of the 

 postero-external lobe. The external faces of the outer lobes, concave transversely, 

 exhibit a comparatively feeble median ridge, of variable distinctness in different 

 skulls. The inner lobes conjoin the outer ones at about the basal third of the latter. 

 Their outer face, concave transversely, also exhibits a slight median ridge. The 

 summits of the inner lobes, in the worn and moderately worn teeth, are distinct or 

 separated from each other at the extremities. The contiguous extremities of each 

 pair of inner lobes, after being directed forward and parallel, cease abruptly in the 

 interval of the outer pair of lobes. 



Constituent elements of a basal ridge, rarely continuous throughout, surround the 

 upper true molars, in various degrees of development in different skulls, sometimes 

 being well marked, in other instances being almost obsolete. Usually portions exist 

 between the buttresses of the outer lobes, and also, in festoons, in the intervals inter- 

 nally of the inner lobes. 



