42 



ILLINOIS NATURAL HISTORY SURVEY MANUAL 4 



Fig. 40. — Characters referred to in the key to orders: a, hind 

 foot of opossum; b, lower jaw of opossum, under side; c, rostrum 

 of muskrat, side view; d, rostrum of cottontail, side view; e, skull 

 of bat, top view ; f, skull of horse, side view. 



