Miscellanies. 209 
The dimension of this interesting fossil, the extreme length of the 
skull being two feet four inches, and the extreme breadth one foot 
four inches, amply attest that the species to which it belonged attained 
a magnitude comparable only with some of the gigantic Pachyderms 
or the extinct Megatherium. 
From the structure of the molar ean and eh continuous ee 
of growth, Mr. Owen showed that the Toxodon is referable to the 
Rodentia; but that it differs from the existing animals of that order 
in the number and relative position of the incisors, and in the number 
and direction of the curvature of the molars. ‘The Toxodon again 
deviates from the true Rodentia, and resembles the Wombat, in the 
form of the articular cavity of the lower jaw. It differs from the 
Rodentia and resembles the Pachydermata in the relative position 
of the glenoid cavities and zygomatic arches, and in many minor 
details. In the aspect of the plane of the occipital region of the 
skull, in the form and position of the occipital condyles, in the trans- 
verse extent of the frontal region of the skull, in the aspect of the 
plane of the bony aperture of the nostrils, and in the thickness and 
texture of the osseous parietes of the skull, the Toxodon differs from 
both the Rodentia and Pachydermata, and manifests an affinity to 
the Cetaceous order. 
From these instances of aberrant characters in the 'Toxodon, con- 
sidered as a gigantic Rodent, and which were described in admirable 
detail, Mr. Owen pointed out, that although the teeth, from their 
correspondence with many other important parts of the animal struc- 
ture, and from the the facility of observing them, are highly impor- 
tant and useful zoological characters, yet they are not, in all cases, 
sufficient alone to determine the order to which a Mammifer be- 
longs; and that upon due consideration it will appear, that dental 
characters must yield the precedence to the modification of the organs 
of progressive motion. It may, therefore, be inferred, that those 
orders in the present received systems of Mammalogy, which are 
founded on characters afforded by the teeth alone, are less natural, 
and less important groups, than those which are based on modifica- 
tions of the locomotive extremities; and @ fortiori, on those which 
combine such distinctive characters with equally characteristic pecu- 
liarities of dentition. At present there is no evidence to determine 
what was the nature of the extremities of the Toxodon, but Mr. 
Owen is of opinion, that although it cannot be positively affirmed 
the genus may not be referable to the Muticata of Linneus, yet, 
, Vor, XXXITI.—No. I. QT 
