| OCR Text |
Show 1885.] DR. ST. G. MIVART ON THE ARCTOIDEA. 359 convex antero-posteriorly. It is greatly narrowed behind the last molars, and hardly more relatively prolonged there than in Cercoleptes. The sagittal ridge is rather strong. The mandible shows a coronoid process, which is loftier and arches more over backwards than that of any of the preceding genera. The inferior margin of the horizontal ramus is convex. There is no subangular process. The angle is very small, upturned, and little produced. The phalanges are very broad, and the ultimate ones have, like those of the Cats, large bony sheaths to shelter the bases of the claws. Nevertheless the penultimate phalanges are not laterally excavated. Molar formula = P . \, M . f. The incisors are singularly small. The premolars and molars are very interesting to compare with those of Procyon. They are formed on the same type as are the latter, but present a wonderful exaggeration of their characters, and are exceptionally broad and multicuspidate. The second upper premolar is a rather large tooth with minute cusps on either side of the base of its great outer cusp, and it has an internal cingulum. The third upper premolar has three outer cusps which are continuous with an external cingulum. There are two internal cusps, whereof the anterior is much the smaller, and another minute cusp is developed from the internal cingulum. The fourth upper premolar has three outer cusps rather distinct from the external cingulum, two subequal internal cusps, and another good-sized cusp developed from the internal cingulum. The first upper true molar has two external and two internal principal cusps, a strong internal cingulum, and an external cingulum with two supplementary cusps and two vertical ridges. The supplementary cusps are placed one in front of and the other behind the antero-external principal cusp. The two vertical ridges descend and lose themselves upon the outer surface of the postero-external principal cusp. The second upper true molar has four main cusps with three external small ones developed from the external cingulum, and one internal cusp developed from the internal cingulum. The first lower premolar is minute and deciduous. The second is like a diminished fourth inferior premolar of Procyon, with the minute supplementary hinder cusps added to it. The third is still more like the fourth lower premolar of Procyon. The fourth is also like it, only that the first cusp is developed almost to an equality with the second, while the third and fourth cusps of the Procyon tooth are represented by a single cusp, which is also almost as large as the second cusp. There is also a median internal cusp. The first lower true molar is like the corresponding tooth of Procyon, but with the hindmost internal cusp represented by two small cusps, as it sometimes is in Procyon. The second lower true molar is like the first, except that the antero-internal cusp (i. e. the most anterior cusp of all) of the latter has disappeared, while an additional, median, large cusp appears at the hindermost part of the tooth. 24* |
