436 



Stultz is dealing with a structure which is 

 developing relatively and actvially later than 

 the forelimb and therefore will show vari- 

 ants from its pattern. It is remarkable that 

 the course of events is so similar when the 

 differentiation time is so widely separated. 



THE LIMB AND GIRDLE IN REPTILES 



The amphibian embryos have served as 

 the tool for most of the experimental analy- 



Special Vertebrate Organogenesis 



ses. A critical morphological study of the 

 development of the forelimbs and hind- 

 limbs and their girdles in Lacerta has been 

 completed by Romer ('42, '44). The first 

 stage which he treats shows the develop- 

 ment of the limb-girdle mass in an embryo 

 of 5 to 6 mm. crown-rump length. It is 

 more advanced in development than is the 

 case in Amblystoma, for the mesenchyme 

 composing the limb bud is perceptibly 

 thicker and consists of three layers ar- 



VI VII VIII IX 





Fig. 155. 



