PRINCIPLES OF ANIMAL BIOLOGY 73 



at their proximal end. What do they represent? Which nodule is the 

 larger? Does this relative size signify anything? 

 In what geological time did Hypohippus exist? 



4. Study the fore or hind foot of Merychippus. Compare in length 

 with the fore foot of Hypohippus. Did the lateral toes reach the ground? 

 Are there any indications of the first and fifth digits (cf . Hypohippus) ? 

 How recent is Merychippus? 



Draw a foot of either Hypohippus or Merychippus. If Hypohippus 

 is selected for this figure, view it obliquely from the side so as to include 

 the vestige of one of the lateral metacarpals. Represent the individual 

 bones carefully in their proper proportions. 



5. Foot of Hipparion or Pliohippus. Compare in height with Mery- 

 chippus. How well developed are the second and fourth digits? Com- 

 pare with Hypohippus and Merychippus. 



Geological period? 



6. Equus, fore or hind foot, either fossil or modern. Compare in 

 size with the earlier forms. Look for vestiges of the second and fourth 

 digits. 



Draw the fore or hind foot of Hipparion or Pliohippus or Equus with 

 care. Turn in such a position as to show one splint bone. 



The Teeth and Skull. 



1. Examine the skull of Eohippus. Note size of the jaws. Note 

 position of orbit of eye relative to teeth. Ask for a specimen, photograph 

 or cast of a tooth of Eohippus. What is the relative length of the crown 

 and the roots? (Note whether the roots are entire or not). Observe 

 the tuberculate surface of the tooth (that is, the cusps or prominences on 



it). 



2. Study the skull of Mesohippus. Compare with Eohippus. 

 Where is the orbit relative to the teeth? A fossil tooth, photograph or 

 cast will be furnished. What is the relative length of crown and root? 

 What is the nature of the surface? Draw the tooth of Mesohippus, either 

 from the original or from a cast or photograph, showing as accurately as 

 possible (a) the length of crown and root, and (6) the form of the upper 

 surface. Shading is desirable to show the latter feature. View the tooth 

 obliquely so as to include roots and upper surface in one figure. 



3. In specimens, casts, or photographs of the tooth and skull of Mery- 

 chippus, note (a) the size of jaw, (6) position of orbit, (c) the size of the 

 crown of the tooth, (d) the character of the surface of the tooth. Draw 

 the tooth of Merychippus or copy the photograph in a line drawing. 



4. Compare the skull and teeth of Equus (either fossil or modern) 

 with the preceding forms. Examine a bisected tooth and note the ex- 

 tent of the pulp cavity. Draw the tooth of Equus in oblique view to 

 show roots and upper surface in one figure. 



