TOXODONT TEETH 



WJ** 3 



For convenience in discussing the modifications of the 

 toxodont tooth, I have, throughout, used the nomenclature 

 illustrated in fig. 52, taking one of the most complicated to 

 -* ;. show the ultimate development. In 



the upper tooth there is, first, the 

 external wall, from which springs 

 the anterior lobe, always the larger 

 lobe, and composed of the protocone 

 and paracone of Osborn. In the 

 rear is a smaller narrower pos- 

 terior lobe, composed of the hy- 

 pocone, the metacone, and the 

 metaconule of Osborn. Between 

 these is a large basin, which may 

 be subdivided by two cristae into 

 secondary bays, referred to as bays 

 I, 2 and 3, while the cristae are in 

 the same way referred to as cristae 

 I and 2. In some genera, the cristae 

 are entirely wanting, in others in- 

 cipient. When fully developed, they 

 are most marked in young individ- 

 uals and, as the tooth is worn, appear progressively shorter. 

 Behind the posterior lobe, there is a variable bay, number 4 

 which is bounded behind by crista 3, which is apparently 

 a development of the posterior cingulum. This last crista 

 and bay may or may not be present. 



The lower molars of toxodonts are all on the same plan, 

 each tooth being composed of two crescents, the anterior 

 and posterior. The ends of these crescents are referred to 

 as the anterior, median and posterior horns. The bay in 

 the anterior crescent is simple and usually disappears with 

 the wear of the tooth without making a pit. In the centre 

 of the posterior crescent is the pillar or posterior tubercle 

 which Scott has found to be characteristic of these South 

 American Ungulates. It is, to my mind, the same as the 





