XTII 



PHYLUM CTTORDATA 



527 



ex oc 



a lonf,'', narrow rostrum, with the 

 external nares at its extremity. The 

 olfactory fossa^ are greatly developed. 

 The rostrum is composed of mes- 

 ethmoid, vomer, maxilhe, and nasals 

 — the premaxillu' being very small. 

 The zygoma is incomplete, and the 

 orbit is not closed behind by bone, 

 the post-orbital processes of the 

 frontal being entirely absent. The 

 "^pterygoids" {ytcr.), in all but Cyclo- 

 tnrus, develop palatine plates. There 

 is no bony auditory meatus. The 

 mandible is entirely devoid of 



consisting of two 

 and slender horizontal rami, 

 with a very short symphysis. 



In the Sloths (Fig. 1140) the 

 cranial region is elevated and 

 rounded, the facial short ; the 

 frontal region is elevated, owing to 

 the development of extensive frontal 

 air-sinuses. The premaxillge are 

 small, and not firmly connected 

 with the maxillgp, so that they are 

 commonly lost in the macerated 

 skull. The jugal (ju.) develops a strong zygomatic process which 



ascending ramus 

 lonof 



fi.mcujc 



Fio. 113'J.— SkviU of Anteater (J-Iyrme- 

 cophaga), ventral view. Letters as iij 

 Fig. 1138. hi addition, li.or. basi- 

 occipital ; glen, glenoid surface for 

 niandihlc ; pter. " pterygoid." 



nrvcLX' 



S.oc 



Fif!. 1140.— Skull of Tbree-toed Sloth {Bradyp^is tridactylv.s). Letters as in Fig. 1 



bifurcates behind into two branches, neither of which is connected 

 with the rudimentary zygomatic process of the squamosal, so that the 



K K 2 



