MUSEUM OF COMPARATIVE ZOOLOGY. 243 
Ropgentia. Lagomorpha. —In the Hare, at the posterior portion of 
the inter-orbital septum, the foramen, which serves as a common outlet 
of the optic nerves, is sufficiently enlarged to constitute a vacuity. 
There are also large vacuities extending from each orbit into the 
latero-nasal regions; these being covered externally by the singularly 
reticulated plate of the maxilla. (Plate I. Fig. 3, a, 6.) Pre- and post- 
palatine deficiencies reduce the palate itself to a mere narrow bridge 
extending across between the premolars. 
Sciuromorpha.—In the Sciuridz, there is a small orbito-nasal defi- 
ciency. In Castor fiber there are large anterior tympanic spaces. 
Myomorpha.— The anterior root of the zygoma presents a vacuity 
in very many of the Rodentia (Plate 1. Fig. 4 a), and in the Rats gen- 
erally this is vertical and dilated superiorly. In Fiber zbethicum, the 
malar vacuity is large, and there is also one in the posterior process of 
the squamosal (Plate I. Fig. 4 6), which is also present in several of 
the Muridz. In Lagostomus, a thin bony plate separates the infra- 
orbital foramen from the antorbital vacuity. 
Hystricomorpha.—In the Porcupines generally, and especially in 
Erethison dorsatus, the infra-orbital as also the ante-tympanic vacuities 
are large. In the Capybara, the former is immense. In Chinchilla a 
large deficiency also occurs in the parasquamosal region between the 
alisphenoid, parietal, and tympanic. (Plate I. Fig. 5, a.) In Paca, the 
foramina, rotundum, and lacerum anterius combine to form a capa- 
cious orbito-nasal vacuity. 
Carnivora. Pinnipedia. Phocide. — Large latero-posterior basal de- 
ficiencies occur in all, while in some, as in P. witulina, P. greenlandica, 
and P. fetida, there is in addition to these a more or less extensive per- 
foration in the basioccipital. (Plate I. Fig. 6, 6.) In the orbito-nasal 
region, not only is the spheno-palatine foramen much enlarged, but a 
deficiency occurs at the juncture of the maxilla, palatine, and frontal, 
often attaining a large size. (Plate II. Fig. 7, a.) 
Otariide.— The foramen lacerum posterius is much enlarged, while 
the orbito-nasal vacuities are extensive, in this family. In Zalophus 
and Callirhinus, in addition to the above, there are large vacuities at 
the juncture of the vertical plate of the palatine with the alisphenoid and 
orbitosphenoid. (Plate II. Fig. 7, 6.) 
Rosmaride. — In the Walruses there are large orbito-nasal and pos- 
terior tympanic vacuities, while the anterior root of the zygoma is 
largely dilated. 
Fissipedia. — In this sub-order, with very few exceptions, no vacuities 
