362 AN INTRODUCTION TO THE STUDY OF FOSSILS 



Fig. 156. — A thirty -foot -long dinosaur, 

 Stegosaurus ungidatus Marsh, abundant 

 during the Jurassic period upon the 

 lands now occupied by the Rocky Moun- 

 tains long before their upheaval into 

 the present mountain system. A, entire 

 skeleton. There should most probably 

 be double the number of large bony plates 

 represented here, arranged in alternat- 

 ing rows, as in Fig. 155. Note the broad 

 attachment of the rib to the back bone 

 for the support of the heavy bony plates. 



B, ideal section through the neck, and 



C, through the trunk of the animal, b.pl., 

 bony plates, in life covered with horn ; 

 ca., carpal bones; co., coracoid, c.sp., 

 caudal spines; fe., femur; fi., fibula; 

 h., encasing-horn ; il., ilium; is., ischium; 

 p., transverse processes; ph., phalanges; 

 pi., bony plate; pu., pubis; r., rib; 

 ra., radius; s., scapula; ta., tarsal bones; 

 /?., tibia; «/., ulna; t)., vertebra. (^, from 

 Marsh ; B, C, from Lull.) 



