60 Geological Society. 
same in Tetracaulodon as in Mastodon, varying in both in its relative 
position to the teeth as these alter their position in age. 
When the striking modifications by which the lower jaw of the 
Elephant differs from that of the Mastodon are considered, it cannot 
be supposed, observes Mr. Owen, that no corresponding differences 
should be present in the lower jaws of the Mastodon and of an- 
other genus of Proboscideans characterized by a difference in the 
number of the teeth, and he says, he knows of no analogy in the 
whole mammalian series that would justify such a belief. Tetra- 
caulodons are as numerous in Mr. Koch’s collection as Mastodons, 
yet there are not found in it two forms of humeri, ulne, radii, 
femora or tibiz, only the merest difference of variety being de- 
tectable; whilst the femora of the Elephas primigenius associated 
with them are at once recognizable by modifications which might 
be expected to accompany true generic differences in the rest 
of the organization. With the exception of a few bones of the 
Elephas primigenius, all the other remains of proboscidian Pachy- 
derms in Mr. Koch’s collection, Mr. Owen is of opinion, belong to 
the Mastodon giganteum; and the great skeleton he considers to be 
that of a male individual, on account of the size of the tusks and the 
strongly marked external characters of the principal bones of the ex- 
tremities ; but he points out that the lower jaw belonged to afemale, 
and he states that the proprietor acknowledged that it was not 
discovered with the other portions of the skeleton. The true height 
of the animal, taken at the dorsal spines, Mr. Owen estimates at ten 
feet, and the length, from the intermaxillary bones to the end of 
the sacrum, at sixteen feet, or four more than that of the Asiatic 
Elephant in the Hunterian Museum. 
The supposed spinal column of a man fourteen feet high, Mr. 
Owen refers to the Lophiodon: Mr. Koch’s collection also includes 
some interesting remains of the Mylodon Harlani, also portions of 
large species of Bos, Cervus, &c. 
With respect to the use of the lower incisor, Mr. Owen says, if in- 
deed this diminutive inferior tusk were a generic character constantly 
associated in both sexes with the enormous upper tusks, no explana- 
tion could be given of so apparently useless an appendage ; but if re- 
garded as a sexitil character, there are in the animal kingdom abun- 
dant examples of the functional importance of external distinctions 
in the male ; and such he considers to be the explanation of the per- 
sistent single or prominent tusk in the male Mastodon. Further, 
with respect to the question why two tusks should be originally de- 
veloped, especially in the female, in which neither is to be retained, 
Mr. Owen replies that there is an equal difficulty with respect to 
the two rudimental tusks in the female Narwhal, and of the single 
one in the male; to the abortive incisors in the symphysial part of 
the lower jaw of the Dugong; to the rudimental teeth in the lower 
jaw of the Foetal Whale-bone Whale; and in the upper jaw of the 
Sperm Whale. In these, and many analogous instances, the author 
observes, a structure which is merely sketched out, and is function- 
less in one species, is perfected and performs important uses in an- 
