'K^^/ 



Fig. 127. Skulls of vertebrates 



Compare the size of the face and jaw with the size of the brain box. Note the ap- 

 pearance in man of a distinct chin and a nose bridge. /, alligator, 18 inches long; 

 2, chicken, i^ inches; 3, lion, 11 inches; 4, lemur, 3 inches; 5, gibbon, 5 inches; 



6, man, 8 inches 



b 



W 



Fig. 128. The third eyelid 



The little fold of tissue extending from the inner corner of the eye corresponds to the 

 third eyelid, or nictitating membrane, in birds and certain reptiles and amphibians. 

 The nictitating membrane can be drawn over the eye so as to cover it completely. 

 a, eye of ape; b, eye of owl; c, human eye; c^, the semilunar fold, eyeball removed 



