GENERAL LAWS OF ANIMAL STRUCTURE. 257 



one treads tiptoe, the other on the tip of the toe. 

 These may be called unguligrade. This becomes the 

 more striking when, as in the horse, the tread is on the 

 tip of the last joint of the one toe. We look with won- 

 der and delight at the danseuse pirouetting on the tip of 

 one toe. The horse is doing this all the time. 



4. M anus and Pes.- — There are two senses in which 

 we may use the term foot. (1) We may use it as that 

 part on which the animal treads. This is the functional 

 or analogical sense. Or (2) we may use it as that part 

 which corresponds to the foot of man, monkey, bear, 



Fig. 164. — Restoration of Rhamphorhynchus phyllurus (after Marsh). 

 One seventh natural size. 



reptile — the original foot. This is the morphological or 

 homological sense. It is in this latter sense that we use 

 it in comparative anatomy. In this sense the horse's 

 foot is eighteen inches long, and the hand of the largest 

 flying dragon [Pteranodon ingens) was fully seven or eight 

 feet long (Fig. 164). In order, however, not to violate too 

 flagrantly common usage, comparative anatomists use the 

 Latin terms manus z.x\A pes to signify all that corresponds 

 to the hand and foot of man and plantigrade animals. 



5. Classification of Ungulates by Foot Structure. — The 

 ungulates or hoofed animals are divided by foot struc- 



