‘ZAPODIDH—ZAPUS HUDSONIUS—CRANIAL CHARACTERS. A69 
supplementary foramen or nick just beneath; the extension of the malar 
bone up the slender styloid zygomatic portion of the maxillary till it sutures 
with the lachrymal, and the slenderness and depression of the rest of the 
zygomatic arch ; the shortness and transverse position of the bullae auditorie ; 
the position of the maxillo-palatine suture; expansion of the posterior nares, 
&e. The skull, as a whole, is shorter for its width, though the zygomata are 
more nearly parallel ; it is also deeper for its other dimensions, with a greater 
degree of convexity, both lengthwise and crosswise, of the superior contour. 
Nevertheless, its general superficial resemblance to that of Mus proper is evi- 
dent. Compared with that of Mus musculus, which is of about the same size, 
we see in each species the same general shape and delicate papery condition, 
without strong angularity, as well as many close coincidences in detail, indi- 
cating that the Murine affinities of the animal are with typical Mus, Hespero- 
mys, &c., and not with the Arvicoline group of Murida@, in which the skull is 
notably heavier, more massive, and more angular. 
As to the general shape of the skull, there is little to be added to the 
foregoing, except such points as, being equally applicable to the familiar Mus 
musculus, need not be recapitulated; we may therefore at once proceed to 
details, in giving which I frequently compare the skull with that of Mus to 
indicate its departures from ordinary Murine features. 
The anteorbital foramen, which transmits the masseter in this instance, 
and which constitutes a prime peculiarity of the skull, is of great size and 
obliquely oval in shape. Instead of being circumscribed by a plate of bone, 
as in Muridg, it is defined externally by a very slender styloid process of the 
maxillary, which is strengthened by the upward extension of the malar, 
applied as a splint along its whole length. Below this main foramen there is 
another much smaller one, which transmits the nerve. This is sometimes a 
complete foramen, separate from the other; sometimes only a deep notch in 
the lower border of the main opening; and this difference niay be observed 
on the two sides of the same skull. I am ready to believe that this lesser 
‘“anteorb- 
opening, giving passage to the superior maxillary nerve, is the true 
ital” foramen itself; for it seems to correspond to the lower part of the large 
slit which, in Muride, is walled in by the maxillary lamina, and it is’ formed 
by a little plate of bone, which rises as a ridge from the alveolar portion of 
the jaw, and bends over to abut against the main wall-of the maxillary. In 
eases in which this plate fails to reach the main wall of the maxillary, so that 
