408 



Family Sciurida. 



Genus Pteromys. 



Dental formula : t g> P H* m S= 22 - 



2263. A mutilated skeleton of the Virginian Flying-Squirrel (Pteromys volucettd). 



It is chiefly remarkable for the long and strong accessory cartilage projecting from the 

 ulnar side of the carpus, which aids in supporting the lateral fold of integument serving as a 

 parachute to support this light and delicate species of Rodent, in its long flight-like leaps 

 from bough to bough. Increased stiffness and resistance are imparted to the bones of the 

 arm by the anchylosis of the radius and ulna at their distal halves. The tibia and fibula are 

 similarly united. The antorbital vacuities are reduced to minute foramina, and present the 

 opposite extreme in this species to their condition in the Cavies and Porcupines. 



Mus. Brookes. 



Genus Sciurus. 

 Dental formula as in Pteromys. 



2264. The skeleton of the Great Squirrel of Malabar (Sciurus mazimus). 



The vertebral formula is : 7 cervical, 13 dorsal, 6 lumbar, 3 sacral, and 24 caudal. In the 

 cervical series only the second and the seventh vertebrae have spines. The transverse pro- 

 cesses of the seventh are imperforate. The spines of the seven anterior dorsals are subequal, 

 the rest gradually diminish in length : that of the eleventh is the one towards which the 

 spines of the other trunk-vertebrae converge. The ridge developed upon the diapophysis of 

 the seventh dorsal rapidly expands in the succeeding ones, and divides in the tenth : the 

 metapophysis and anapophysis become distinct in the eleventh, and are continued throughout 

 the lumbar series. Seven pairs of ribs directly join the sternum, which consists of six bones. 

 The acromiou is bent almost at right angles with the spine of the scapula, and it terminates 

 in three prominences : the coracoid is unusually long. The clavicles are entire. The humerus 

 is perforate above the inner condyle, but not between the condyles. In the femur the small 

 trochanter is unusually prominent : there is also a trochanterian ridge below the base of the 

 great trochanter. 



Mus. South. 



2265. The skull of the Sciurus maximus. 



The occipital region is low and broad. The paroccipital and mastoid processes are small, 

 but distinctly developed, the paroccipitals being the longest. The occipital condyles are 

 slender. The auditory bullse are large, the meatus appearing as a circular piece cut out of 

 the wall, which is not prolonged into a tube. The posterior process of the squamosal is 



* The anterior of these premolars is small, and is soon shed. 



