XIII 



PHYLUM CHORDATA 



495 



ex.oc 



of mesethmoid, vomer, maxilla3 and ^ oc 



nasals the premaxillae 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 (pter.) in all but 

 Cycloturus, 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. 1071) 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 premaxilla3 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 bi- 

 furcates behind into two branches, 

 neither of which is connected with 

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



FIG. 1070. Skull of Anteater (Myrme- 

 cophaffa), ventral view. Letters as in 

 Fig. 1069. In addition, b.oc. basi- 

 occipital; glen." glenoid surface ; for 

 mandible ; ptervpterygoid. 



S.0C 



FIG. 1071. Skull of Three-toed Sloth (Bradypus tridactylus). Letters as in Fig. 1069. 



zygomatic arch remains incomplete. There are, at most, the rudi- 

 ments of post-orbital processes of the frontals. The pterygoids 



