STRUCTURE OF PLESIOSAURIAN PROFODIAL 



403 



with the same curious development of the articular ends as 

 in the propodium. From what we know in the development of 

 mammalian long bones it would be expected that all long 



Fig. 1. Femur (propodial) of Ogmodirus martinii, Williston and Moodie, 

 from the Cretaceous of Kansas. X .5 



Fig. 2 A longisection of the distal portion of an embryonic plesiosaurian 

 propodial, showing the sharply marked cone at A indicating a distinct differ- 

 ence in the rate of growth in the peripheral, or perichondral, and the secondary 

 or endochondral bone. The cone-shaped structure A has been called an epiphysis. 



bones in the extinct reptiles should exhibit these characters. 

 Further study of this problem will doubtless result in the 

 discovery of these characteristics in all of the plesiosaurian 

 long bones, especially in young and immature animals. 



JOURNAL OF MORPHOLOGY", VOL. 27, NO. 2 



