Professor Owen’s Report on the Missourium. 61 
Pp 
other closely allied. ‘Thus the teeth which are shadowed forth in 
the lower jaw of the Feetal Whale are fully developed in the Cachalot. 
The upper rudimentary maxillary teeth which remain hidden in the 
gum of the Sperm Whale are functionally developed in the Grampus; 
and in like manner in the gigantic Dinotherium, discovered by Dr. 
Kaup, is exhibited the full and functional development of the infe- 
rior rudimental tusks of the Mastodon. 
The molar teeth of the Mastodons offer, Mr. Owen says, a beauti- 
ful transitional modification connecting the lamellated structure of 
the triturating molar with those having simply a transversely-ridged 
grinding surface. The interval between the molar teeth of the 
Elephant and those of the Tapir is too great to have allowed their 
fundamental resemblance to have been detected in the existing 
creation; but a study of the extinct Pachyderms brings to light, 
he says, a beautiful series of gradations leading through the ele- 
phantoid Mastodon of Ava and the gigantic Mastodon of the 
Missouri to the Dinotherium, which it may be remembered was the 
gigantic Tapir of Cuvier. Moreover, he adds, the indication of the 
singular armature of the lower jaw of the Dinothere might be most 
closely discernible in that species of Mastodon which makes the 
nearest approach to the Dinothere in the form of the grinding teeth. 
The report from which the above extracts have been taken had been 
completed when Mr. Owen received a copyof the notice* of Dr. Hays’s 
description of Mr. Koch’s collection. After an attentive perusal of 
this document, in which the generic distinctness of the Tetracaulo- 
don is maintained, Mr. Owen has been only more convinced of the 
truth of his own theory ; he, however, in justice to Dr. Hays, gives 
the arguments of that esteemed naturalist. Dr. Hays considers the 
existence of a single tusk in the lower jaw to be only an accidental 
occurrence, referring, as examples of two tusks, to the specimen 
described by Dr. Godman, and to that belonging to the Museum of 
the University of Virginia. Respecting this statement, Mr. Owen 
observes, that the jaw described by Dr. Godman is that of an im- 
mature individual, retaining on the left side the first small molar, 
and therefore affords no proof of the persistence of the two in- 
ferior tusks in the adult animal, or evidence of the accidental na- 
ture of the absence of the left tusk in the mature jaw. With regard 
to the specimen in the cabinet of the University of Virginia, he 
says, that if this belong to a mature animal it would be an unique 
specimen, and might be paralleled with cases on record of two 
projecting tusks in the male Narwhal, and considered by all na- 
turalists to be accidental. Mr. Owen further calls attention to the 
figure of the specimen in pl. 27. fig. 2. of the Transactions of the 
American Philosophical Society (vol. iv.), where only the right tusk 
is represented, the left being merely indicated by a dark spot of cor- 
responding size, of the nature of which the text is silent. 
Respecting the symphysial portion of the jaw exhibiting the alve- 
oli of two tusks, both much smaller than the alveolus of the right 
* Proceedings, American Phil. Soc. October 1841, 
