TOXODONT TEETH 87 
For convenience in discussing the modifications of the 
toxodont tooth, I have, throughout, used the nomenclature 
ilustrated 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 
1, 2 and 3, while the cristae are in 
the same way referred to as cristae 
ITand2. Insome genera, the cristae 
are entirely wanting, in others in- 
soon; 2, Tower molars, somewhat eipient When f ully 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 
lobe 
Posterior 
vista 3 
