MUSEUM OF COMPARATIVE ZOOLOGY, 243 



RoDENTiA. Lagomorplia. — 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, b.) Pre- and post- 

 palatine deficiencies reduce the palate itself to a mere narrow bridge 

 extending across between the premolars. 



Sciuromorjiha. — In the Sciuridse, 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 I. Fig. 4 a), and in the Rats gen- 

 erally this is vertical and dilated superiorly. In Fiber zibethicum^ the 

 malar vacuity is large, and there is also one in the posterior process of 

 the squamosal (Plate I. Fig, 4 b), which is also present in several of 

 the Muridae. In Lagostomus, a tliin bony plate separates the infra- 

 orbital foramen from the antorbital vacuity. 



Hystric.omorpha. — 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. Pinniped ia. Phocidce. — Large latero-posterior oasal de- 

 ficiencies occur in all, while in some, as in F. vitidina, P. groenlandica, 

 and F. fcetida, there is in addition to these a more or less extensive per- 

 foration in the basioccipital. (Plate I. Fig. 6, b.) 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.) 



Otariidce. — The foramen lacerum posterius is miich 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, b.) 



Rosmaridce. — 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 



