00 LEONARD W. WILLIAMS 



end of the following centrum. Goette believes that these ele- 

 ments, namely the centrum, the intercentrum, the two pairs of 

 neural and the single pair of haemal arches, unite with one another 

 in several ways with the abortion or enlargement of certain units 

 so as to form the various types of vertebrae occurring in Digitates 

 and in the Amiidae among fishes! 



Manner ('99) found two pairs of cartilaginous neural arches 

 in Angius and Lacerta; and Schauinsland ('00) discovered two 

 pairs of cartilaginous neural arches in the caudal region of embryos 

 of Hatteria. In embryos which were about to hatch, he found 

 conditions similar to those described by Goette in Lacerta. How- 

 ever, in Hatteria not only are the neural arches and transverse 

 processes double, but the centrum also shows indications of the 

 same structure because, as Schauinsland believes, it arises from 

 parts of the sclerotomes of two adjacent segments. Goette, 

 however, does not maintain that the centrum is double, but 

 that, corresponding to each segment, there are two axial 

 elements, — the centrum, which is intersegmental, and the inter- 

 centrum, which is midsegmental in position. Schauinsland 

 regards the subnotochordal bar (hypochordale Spange) of Froriep 

 as the haemal arch. 



After Remak had shown that the Urwirbel or protovertebra 

 contains anlagen of the body musculature as well as of the ver- 

 tebrae, the name became inappropriate; nevertheless, it was used 

 without question until Goette in 1875 proposed to use the term 

 segment. A few years later in the second edition of Foster and 

 Balfour's "Textbook of Embryology" ('83) the term mesoblastic 

 somite, or somite, was used as a substitute for the name pro- 

 tovertebra. It seems best to denote by the word somite one of 

 the blocks of mesoderm formed by the segmentation of the verte- 

 l)ral or somitic plate and to make the segment include a pair of 

 somites with the corresponding nephrotomes. 



While Von Ebner was discussing the intervertebral fissure and 

 resegmentation, Kabl ('88), demonstrated that the dorsal lamella 

 or muscle plate of Remak becomes a two-layered plate, the Haiit- 

 muskelplaiie (dermomyotome) and that the inner layer only, the 

 Muskellamelle (myotome) forms muscle, whereas its outer layer. 



