16 



unpaired between the medial ends of the claviculae. Götte holds 

 tiie opinion that, also on account of its paired formation, the epis- 

 ternnm develops from a part of the clavicular formation which is 

 bent caudallj- Moreover, in his opinion, the clavicle originates as a 

 blastemic process of the primary shoulder-girdle. Gegenbacer '), on 

 the contrary holds (hat the connection of the clavicle and shoulder- 

 girdle is a secondary one. Hoffman ■) observed the paired development 

 of the epislernuin in the crocodile, and also on the basis of Götte's 

 researches, he speaks of a clavicular sternum. Wiedersheim was not 

 able to fintl any real genetic connection of the episternum with 

 the clavicula either in Lacerta or in Crocodilus, although lie suc- 

 ceeded in recognizing the clavicula, the embryonal existence of 

 which Götte had already surmised in a rudimentary form. As 

 regards the relation between the clavicula and the .scapulo-coi'acoi- 

 denm, Wiedersheim shares Gütte's opinion. Schauinsi.and ') did not 

 ünd in Sphenodon any primary connection of episternum and clavi- 

 cula in stadia where the medial portion of the latter contained no 

 bone as yet. Besides a primary connection of clavicula and scapulo- 

 coracoideum Bogoi.jubski mentions a paired formation of the epister- 

 num, in which the ossification takes place fiom paired centra. Of 

 the genetic relations of clavicula and episternum he gives no details. 



None of the researchers ever found any cartilage in episternum 

 and clavicula. Götte and Wiedersheim, however, describe a form of 

 ossification which is strongly suggestive of the formation of perichon- 

 dral bone round about a nucleus of cartilage. The bony clavicle, 

 (hey say, first canaliculate and afterwards cylindrical, enclosing a soft 

 medullar cord, just like a cartilaginous process. Schauinsland and 

 BoGOLJUBSKi specially mention to have found no trace of such a 

 peculiar ossification process. According to these writers the medullar 

 cavity is produced by osteoklastic action. 



1 had for my investigations seventeen embryos of the common 

 lizard, lacerta agilis, all of which 1 prepared in cross-sections. 

 (Section thickness 10 f*). Further, the collection belonging to the 

 Anatomic Laboratory contained a dozen series of Gongylus ocellatus 

 and two of Ptychozoon homalocephaluni. The direction in which 

 sections were made in the tliorax-region depended intimately upon 

 the age of the embryos, namely, they were all made frontal on the 

 jaw. This, with the slight curve in the region of the neck in the older 



1) C. Gesenbaur, Untersucli. z. Vergleich. Anat. der Wirbelthiere. 2 Teil. 

 Schultergürtel. Leipzig 1865. 



•) G. K. Hoffmann, Niederi. Arcliiv. f. Zoölogie, Bd. V, 1879. 



5) H. Schauinsland, Archiv. f. Mikrosk. Anat. u. Entw.gesch. Bd. LVI, 1900. 



