PROFESSOR OWEN ON SOME SPECIES OF THE EXTINCT GENUS NESODON. 297 
of their appearance in other Herhivora, I regard the fifth tooth in place as the first 
true molar {m i of my dental notation*), the succeeding germ to be the second true 
molar {m2), and the preceding four grinders in place as being the deciduous grinders 
{di to 4). At the stage of growth here exemplified, with the crown of the first true 
molar {m 1) only beginning to emerge from its socket, the germs of the vertical 
successors (premolars) of the deciduous molars could scarcely be expected to be 
calcified; but the depth of the jaw beneath those molars, and the space provided by 
their narrow and diverging fangs, indicate a provision for lodging the matrices of 
successional teeth, and the small cavity in the substance of the jaw (fig. 7 , p 4) 
beneath the fangs of the fourth molar {d 4) is probably the beginning of the formative 
nidus of its successor, the fourth premolar {p 4). 
The small size of the incisors, in comparison with the premaxillary bones, and 
their scattered disposition therein, indicate them to belong to the deciduous series, 
to which, also, we must refer the diminutive canine. 
The shape, size, disposition and complex structure of the molar teeth prove the 
present extinct species to be herbivorous, and the number and nature of the teeth 
exposed indicate it to be ungulate. No herbivorous or other Rodent has canines 
and six incisors in the upper jaw; and no Mammal of the Order Bruta {Edentata, 
Cuv.) has deciduous teeth properly so called, or molars divisible into two kinds. All 
the herbivorous Marsupials have a single pair of large procumbent incisors, and no 
canines, in the lower jaw. 
In comparing the fragments of skull and the teeth above-described with the cor- 
responding parts of existing Ungulata, we find the most numerous and important 
correspondences to be with those belonging to the order Perissodactyla\. 
Both upper and lower true molars in the Nesodon have very long crowns, indi- 
cating the roots to be comparatively short, and formed late, as in the genus Equus 
The close imbricated disposition of the upper molars and the pattern of the enamel- 
folds of the crown find their nearest parallel in the Rhinoceros. 
Both the Tapir and the Horse resemble the Nesodon in the number and relative 
proportions of the incisors and canines. The Tapir, amongst existing Ungulata, 
offers the closest resemblance to the Nesodon, in the form and proportions of the 
zygomatic arch, of the widely communicating orbital and temporal fossse, and of the 
articular eminence and cavity for the lower jaw. The premaxillaries join the nasals as 
in the Horse. The proportions and shape of the post-glenoid process in the Nesodon 
approach more nearly those in the Tapir or Horse,than those in any of theArtiodactyles:|; 
in which that process is well-developed, as e.g. the Peccari and Hippopotamus, in 
neither of which is the ‘ eminentia articularis’ developed as in the Nesodon. The 
principal osteological character in which the Nesodon deviates from the perissodactyle, 
and seems to approach the artiodactyle, type, is the production of the osseous roof of 
* Philosophical Transactions, Part II. 1850, p. 491. f Pachydermes d doigts impaires, Cuvier. 
+ Pachydermes d doigts paires et Ruminans, Cuvier. 
