RODENTIA. 



265 



. In the Rodentia, the scaphoid and lunar are very 

 generally united (as in Castor, Dasyprocta, Hydrocha'nts, 

 Capromys, Schirus, Arciomys, Mus, &c), but riot in all. An 

 os centrale is present in many, as Lepus, Dasyprocta, Hydro- 

 chcerus, Capromys, and Castor, while in other genera it is 

 absent. There is very frequently an accessory ossicle on the 

 radial side of the carpus, which is particularly large in the 

 Heaver (Fig. 91). There are nearly always five digits, with 



Fig. 91. — Bones of the manus of the Baaver {Castor canadensis), f. 



the normal number of phalanges, though sometimes (as in 

 Hydrochcerus) the pollex is rudimentary or suppressed. 



In the Cape Hyrax (Fig. 92, p. 266) there is an additional 

 carpal bone (ce), which is probably the os centrale, though 

 in form and situation it looks as if it. were a dismemberment 

 of the proximal part of the trapezoid (td). The scaphoid 





