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embryos, was |iractically identical with frontal on tiie thorax. Ac- 

 cording as ilie neck-curve was more pronounced in tlie younger 

 embryos, tlie sections were made more transverse on the thorax. 

 In the account of my observations 1 sliall commence with Laeerta, 

 as my material of this was the most complete. 



Fig. Irt shows the shoulder-girdle of Lacerta agilis spread out in 

 one flat plane, whereby the sternum and episternum have been left 

 in position in order to show the relative positions. Fig. lb shows 

 only the primary shoulder-girdle. 



C la vi^ c vilcc 



Fig. 1. Sternum and clavicula shoulder- girdle of Lacerta agilis. 



Tlie primary shoulder-girdle, i. e. the cartilaginous preformation, 

 consists of a dorsal portion: the scapula and the non-ossifying large 

 supra-scapula, and a ventral portion, viz. the coracoid. in which we 

 usually distinguish three parts: coracoideum, s. str., procoracoid and 

 epicoracoid. They surround an oval opening, the fenestra coracoidea 

 principalis (Fürbringer) ';. Besides this cranial to the fossa glenoidalis 

 humeralis, there is generally another fine canal, through which the 

 n. muse. so|)racoracoidei runs. This canal will henceforth never be 

 counted among the coracoidal fenestrae (many I'eptiles possess more 

 than one fenestra'.). The cranial border of the primar}- shoulder-girdle 

 exhibits a deep incisura scapulo-procoracoidea which is bridged by a 

 strand of connective tissue, lig. scapulo-procoracoideum. Tiie coia- 



1) M. FüRBRiNGER, Jenaïschs Zeitschr. Bd. 34, 1900. 

 Proceedings Royal Acad. Amsterdam Vol. XXVI. 



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