18 



coideiiin is received (liurlludtirally in tlie sulcus ariicularis coraooi- 

 dalis stenii. The clavicula is connected syiidesinolically witli the 

 snprascapnla. Between the media! e.xtieuiities of Ihe clavicidae the 

 cranral point of the dagger-like episternnin interposes. The latter lies 

 mainly cranial to the sternum ; a small part, however, lies ventral to 

 the steinnm and is quite separated from it hy connective tissue. 



The youngest embryo that I was enabled to examine, Lac.erta 

 ag. D. (N. T.) ') about 22), possessed no shoulder-girdle yet. Only in 

 the inarticulated epiphysal limbbud was a central blastema. Besides 

 the primary shoulder-girdle, also the clavicle was lacking. 



In the embryo Lacerta ag. S. (N. T. about 24) the central blastema 

 of the superior limb has extended proximally as a blastemalie form- 

 ation of the shoulder-gii'dle as yet very difiiculi to define. There 

 is no trace yet of the clavicula. 



The embryos Lacerta ag. E. and F. (N. T., about 26) contain a 

 well defined shonlder-girdle which still consists entirely of dense 

 mesenchyme. 



Any clavicular formation is still lacking. In the humeral formation 

 there is already praechondrium. Tiie line of demarcation of the cora- 

 eoid with respect to the growing sternal formation is much more 

 obscure than it was in embryo S. Specially noteworthy is the fact 

 that the formation of the shoulder-girdle, apart from the nerve-canal, 

 one solid whole. 



Embryo Lacerta ag. 1. (N.T. about 28) is clearly in a more advanced 

 stage of development. Cartilage is found in the humerus, which 

 passes over proximally into praechondrium of which also a part of 

 the primary shonlder-girdle consists. The latter still forms one conti- 

 nuous whole with the humerus. In this embryo Ihe boundaiT of coracoid 

 and sternal formations has almost disappeaied, a transition stadium 

 which will speedily be followed by the formation of the definite 

 articular cavity. In the process of (he primary girdle the [traechon- 

 drium occupies the caudal region ; Ihe rest is still compact mesen- 

 chymalous, but quite homogeneous. 



From the cranial border of the scapulo-coracoideum, dorsal from 

 the humerus-formation a blastemalie spur proceeds. There is also a 

 very small fragment of bone tissue to be seen, quite dorsally close 

 the point of attachment to the primary shoulder-giidle. 



Lacerta ag. K. (N.T. about 29). The line of demarcation between 

 coracoid and sternum is indicated (now permanently) by a loose 

 mesenchymatous layer. There is an increase of praechondrium in 



') K. Peter, Normenlafel Lacerta agilis. 



