590 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
The temporal muscle is of moderate bulk, the fossa being comparatively 
shallow. The masseteric and pterygoid masses are of great size: 'The mas- 
seter forms a bulging mass on the outside of the jaw, completely filling the 
great fossa formed by the outward twist of the angle of the jaw, and defined 
in front by an oblique ridge already described in speaking of the bone. A 
special stout tendon arises from the zygomatic process of the maxillary, just 
below the anteorbital foramen, which latter opening, notwithstanding its small 
size and apparently inconvenient relations, transmits a small fascicle of the 
masseter along with the superior maxillary nerve. 
The muscles acting upon the hyoid bone, both from the thorax and from 
the jaw, are well developed. A pair of stout fusiform muscles connect the 
hyoid with the back of the skull. I find no trace of direct muscular connec- 
tion between the hyoid and the scapula (omo-hyoid). Sterno-mastoid and 
cleido-mastoid are well developed, and distinct from each other for nearly, if 
not quite, all of their extent, though their thoracic insertions are very near 
together. 
The diaphragm is very thin, even its most muscular portions, and a large 
part of it is simply membranous. There is a large, well-defined, central 
“tendon”, as broad as the muscular portion on either hand. This is of oval 
shape in most of its extent, but with two posterior prolongations, one on each 
side, separated by the fleshy “pillars” which arise from the vertebra, and pro- 
ceed to embrace the cesophageal orifice. Muscular fibres are scarcely or not 
developed laterally behind, where simple membrane may be traced to the 
insertion of the organ along the floating rib. The radiating muscular portion 
of the diaphragm, then, is a single set of fibres arranged in fan-shape around 
the anterior oval portion of the central tendon; these fibres are continuous 
on the median line in front. The aortic opening, as usual, is close to the ver- 
tebree; the cesophageal aperture is removed from the spinal column by the 
whole length of the muscular pillars. From the middle line of the diaphragm 
depends a broad peritoneal fold, suspending the liver, to which, more posteri- 
orly, it is closely adapted. 
E.—HISTORY AND HABITS OF THE SPECIES. 
To render the account of this remarkably interesting animal more com- 
plete, I shall, in tracing its history, include some notices of its habits. I have 
already presented those considerations which bear upon the history of the 
genus and family. 
