1847.] OWEN ON EXTINCT ANTHRACOTHERIOID QUADRUPEDS. 105 
rium; the fifth lobe, p, answers to the small internal lobule in some 
Ruminantia, and to its more developed homologue in Anoplothe- 
rium, which is marked p in pl. 134. fig. 5. and pl. 135. fig. 2. of my 
‘ Odontography,’ and in fig. 5 of pl. 3, Quart. Geol. Journ. vol. iv.; 
but which in Hyopotamus is not only larger, but is moved to the in- 
ner and anterior angle of the crown of the tooth. In the present 
memoir this will be described as the fifth lobe, and the others (0, o! 
& i, 7) as the parial or normal lobes of the tooth. The external side 
of each normal lobe is concave, but is deepest in the two outer lobes, 
o, o', fig. 1, and is divided from the other two sides by sharp, curved 
ridges ; the angle between the other two sides is less sharp, and is 
rounded off in the inner and posterior lobe, as it is in the fifth lobe, 
p, both of which thus present a convexity towards the inner or pala- 
tal side of the tooth (fig. 3): the fifth lobe (p) is a rounded cone, 
with one ridge along its outer side; the valley between it and the 
inner and anterior normal lobe, 7, is much less deep than those which 
divide the normal lobes: the summits of all the five lobes are pretty 
sharp, that of the fifth bemg the lowest ; they are worn chiefly down 
the sides of the angles, indicating high-pointed lobes on the lower 
teeth of a size and shape that could penetrate the deep valleys of 
those of the opposing teeth above. 
The outer side of the base of the crown (fig. 2) presents three 
bulging parts, one very large and prominent at the middle, upon 
which the opposite and contiguous angles of the two outer lobes are 
continued and meet, describing a strong curve convex outwards, and 
bounding a deep excavation on its inner side, leading to the deep 
middle transverse valley of the crown: a second protuberance (qa) 
forms the anterior angle of the outer side of the base, and the third 
smallest protuberance the posterior angle of the same side: this side 
of the base is not traversed by any ridge. The outer sides of the 
outer lobes are made hollow by the projection of the three tuberosi- 
ties which render the intervening parts concave ; but above these de- 
pressions the outer sides of those lobes are nearly flat, each being 
traversed there by a very feeble longitudinal median rising. The in- 
ner side of the base of the crown is equally free from any ridge; it is 
formed by the convex sides of the two inner pyramidal lobes, 7 & p: 
a nearly vertical ridge (7) ascends from their interspace upon the an- 
terior surface of the posterior lobe. A very strong ridge traverses 
the base of the anterior side of the crown (fig. 5, f): it is continued 
backwards from the anterior and external angular bulging (a), forms 
a slight angle at each interspace of the three lobes on that side of the 
crown, and thus presents a feebly festooned course, and gradually 
subsides at the anterior and internal side of the crown. A well- 
marked but narrower ridge (h) traverses the base of the posterior 
side of the crown (fig. 4), and rises in a slight angle upon the poste- 
rior ridge of the posterior internal lobe. 
The bases of the four roots are indicated at the fractured part of 
the alveolar process of the jaw which is still attached to this tooth: 
the two external roots were obviously distinct : the two internal and 
smaller roots appeared to have been connate. 
12 
