SKELETON OF BRUTA. 



405 



plate of bone. The alisphenoids join the parietals. The lacrymal 

 is large and chiefly antorbital. The petrosal presents a wide and 

 shallow cerebellar fossa : the canal between the petrosal and the 

 angle of the superocclpital gives exit to a vein and entry to an 

 artery. The rhinencephalic almost equals the epencephalic divi- 



272 



273 



Dwarf Arniadillo {Chlamyphoriis trimcatus). Lxxxviii*. 



sion of the cranial cavity. The frontals are large, but chiefly 

 occupied by the nasal chamber : in the Chlamyphorus the outer 

 table rises into a pair of domes, fig. 272, a, augmenting the olfac- 

 tory cavity. In most Armadillos there are two small prenasal 

 ossicles. The premaxillaries are small and lodge the first tooth 

 in one or two species. The zygomatic arch is complete and 

 strong: the malar part, fig. 271, 27, curves down outside the 

 mandible, and there, in Glyptodon, developes a long process for 

 the service of the masseter. 



The zygomatic arch culminates in regard to complexity in the 

 Sloths, albeit in the small 

 existing species, ^g. 273, the 

 squamosal element, 27, fails, 

 as in the Anteaters, to reach 

 the malar one, 26, b. In the 

 Meo-atherioids this union is ef- 

 fected, fig. 274, and an unusu- 

 ally massive arch is the result. 

 The malar, 26, still sends 

 upward its temporal process, 

 b, and downward its mas- 

 seteric one, a. This cranial 

 developement relates, as in 

 the recent and extinct Kan- 

 garoos, to the share of the masseter in the business of mastication ; 

 and the molars are transversely ridged in Megatherium as in 

 Diprotodon. 



Skull of Ai {Brad, tridactylus), half nat. size. 



