Lect. IV.] SKULL OF SLOTH AND ANT-EATER. 105 



" The wisest aunt, telling the saddest tale," is not a 

 more solemn creature than the Sloth ; and deep 

 in his cranio-facial organisation there is a peculiar 

 structure, one among many of the strange things in 

 the structure of this joyless Puritan of the primaeval 

 forest. 



In us, as is well known, the "internal pterygoid 

 plates " develop a retral hook, the " hamular (hooked) 

 process," and the muscle acting upon the soft palate runs 

 its line or tendon over this hook. In one kind of Sloth 

 this pterygoid bone is very large indeed, and is hoUowed 

 out into a cavern, into which and from which the breath 

 enters, but has no free escape behind ; these caverns run 

 right and left, and each of these may be compared to 

 the " antrum highmorianum " of man. This cavity in 

 the pterygoid of certain Sloths is a structure similar to 

 that which is seen in various parts of the skulls of the 

 higher vertebrata. 



As for the use of these caves, in which the wind sleeps 

 for a time in this sleepy creature, I am somewhat 

 doubtful. 



One great unlikeness of the Sloth to the other Eden- 

 tata, especially the toothless kinds, is seen in the deep 

 malar (cheek) bone ; in the Armadillo this element is of 

 the medium size, in the Pangolin and Ant-eaters it is 

 either suppressed or greatly aborted. In the toothless 

 kinds the temporal and masseter muscles (those that 

 act upon the parts round the mouth) are small, the 



