306 ON THE EXTINCT MAMMALIA OF 



3—3 1—1 7—7 



In. — : can. — ; mol. — = 44 teeth. 



3—3 1—1 7—7 



None of the specimens of A. Bairdi under examination have retained the incisors 

 or canines, but a number with full series of molars, of different ages, have been pre- 

 served. 



The molar teeth of J.. Bairdi are absolutely identical in form with those oi Ancki- 

 therium aurelianense, as represented by De Blainville in his Osteographie, under the 

 name of Palceoiherium hipimdes, in plate vii of the genus Paloeotherium. Well pre- 

 served specimens of series of molars of the latter species, from Sansan, Gers, France, 

 contained in the collection of this Academy, on comparison exhibit the same 

 character. 



The molar teeth of AncMtJierium exhibit so wide a difference from those of the 

 Horse, and comparatively so near a resemblance to those of Palceotherium, that it is 

 not at all surprising that its remains were originally referred to the latter genus. 

 Notwithstanding the difference, attention once directed to the subject, an equine 

 character is distinctly traceable in these teeth. They have short crowns without ce- 

 mentum, and are inserted into the jaws by distinct fangs during the whole period of 

 their functional existence. In the Plorse, the corresponding teeth have long columnar 

 crowns, in the constitution of which cementum enters as an important constituent- 

 The crowns are gradually protruded from the jaws as they are abraded in the process 

 of mastication, and it is only when aged, and the crowns are nearly worn out, that 

 these teeth come to be inserted by distinct fangs. 



Of the upper molar teeth of Ancliiiherium Bairdi, the first of the series, as usual, 

 in comparison with the others is small, but is proportionately large in comparison 

 with that of the Horse. It has a simple conical crown, compressed on the inner side, 

 and measuring three and a quarter lines fore and aft and two and a half transversely. 

 It is inserted by a pair of fangs, appears to retain its position in company with the 

 large molars to the latest period, and is worn away together with them. 



The six large upper molars, as in all other equine animals, are nearly alike in form 

 and size. They have square crowns with the width exceeding the breadth, and with 

 both these measurements considerably greater than the length. They are inserted 

 by four fangs, of which the outer ones are vertical and widely separated, and the 

 inner are confluent and divergent from the others. The crowns are composed of 

 three pairs of lobes, of which the inner and outer are the principal ones, and the 

 median lobes are the smaller and of secondary importance. 



The outer lobes are demi-conoidal, and resemble those of Palceotherium. They 

 form at their conjunction a narrow buttress externally ; and a stronger buttress bounds 

 the fore part of the anterior of the two lobes. A tendency to the development of a 

 buttress is seen also at the back part of the posterior of these lobes. The buttresses 



