PHTLITM OHORDATA 



527 



a long, narrow rostrum, with the b oc 



external nares at its extremity. The 



olfactory fossa? are great!}' developed. 



The rostrum is composed of mes- 



ethmoid, vomer, maxilhe, and nasals 



— the premaxilhv being very small. 



Tiie zygoma is incomplete, aird the 



orbit is not closed behind by bone, 



the post-orbital processes of the 



frontal being entirely absent. The 



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



turus, develop palatine plates. There 



is no bony auditory meatus. The 



mandible is entirely devoid of 



ascending ramus — consisting of two 



long 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 maxillae, so that they are 

 commonly lost in the macerated 

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



fi.ma^x 



Fi.-i. nssi.— Skull of Anteater (il^n-me- 

 ropliagu), ventral view. Letters as in 

 Fig. 1138. In addition, h.oc. ba.si- 

 occipital ; glefi. glenoid surface for 

 mandilile ; pu.r. " pten'griid.'" 



Fir,. 1140.— Skull of Three-toed Sloth (I!ra,r;qiva t,-Uln,:liilu^). Lettor.s as in Fi),'. 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 



