186 



OBSERVATIONS ON THE RODENTIA, 



ofMyoxus avellanarius, now before me, enable me to give the 

 above characters of the present family. 



The general form of the skull of the Myoxidce is interme- 

 diate between that of the Sciuridce and the Muridce ; the in- 

 ter-orbital portion is more contracted than in the Sciuridce, 

 and the nasal bones are proportionately narrower and more 

 elongated. The species of the present family are readily dis- 

 tinguished from the Sciuridce by the want of a post-orbital 

 process and the larger size of the ant-orbital foramen, which, 

 instead of being placed far forward and low down, is situated 

 in the thin plate which forms the zygomatic process of the 

 maxillary bone. 



The larger size of the ant-orbital foramen and the imper- 

 fect state of the palatine process of the palate-bone, lead us 

 to the Jerboas {Dipus), where the form of the jaw bears a re- 

 markable resemblance to that of Myoxus, as will be seen. 



The genera Myoxus and Graphiurus contain all the spe- 

 cies I am acquainted with belonging to the Myoxid®. 



Family III. — G-ERBOiDiE. 



or 



Dentition. — Incisors laterally compressed, muiaio T 

 -§-§-) rooted and unequal in size ; the series on each side of 

 each jaw parallel and widely separated. 



(a) Skull of Dipus hirtipes, seen from above. (6) the same seen laterally. (c) skull of 



Dipus sEgyptius, seen from beneath {d) ramus of lower jaw of ditto, inner side. 



Skull. — Palatine portions of the intermaxillary, maxillary, 

 and palatine bones on the same plane, or nearly so. Inci- 



