THE VERTEBRAL COLUMN. 371 



(PI. 18, fig. i). Small portions of several muscle-plates come in 

 this way to be situated in the limbs, and are very soon seg- 

 mented off from the remainder of the muscle-plates. The por- 

 tions of muscle-plates thus introduced into the limbs soon lose 

 their original distinctness, and can no longer be recognized in 

 stage L. There can however be but little doubt that they 

 supply the tissue for the muscles of the limbs. The muscle-plates 

 themselves after giving off these buds to the limbs grow down- 

 wards, and by stage L cease to shew any trace of what has 

 occurred (PI. 13, fig. i). This fact, coupled with the late develop- 

 ment of the muscles of the limbs (stage O), caused me to fall 

 into my original error. 



The Vertebral Column and Notochord. 



In the previous chapter (p. 325) an account was given of the 

 origin of the tissue destined to form the vertebral bodies; it 

 merely remains to describe the changes undergone by this in 

 becoming converted into the permanent vertebra;. 



This subject has already been dealt with by a considerable 

 number of anatomists, and my investigations coincide in the 

 main with the results of my predecessors. Especially the re- 

 searches of Gegenbaur 1 may be singled out as containing the 

 pith of the whole subject, and my results, while agreeing in all 

 but minor points with his, do not supplement them to any very 

 great extent. I cannot do more than confirm Gotte's 2 account 

 of the development of the haemal arches, and may add that 

 Cartier 3 has given a good account of the later development of 

 the centra. Under the circumstances it has not appeared to me 

 to be worth while recording with great detail my investigations; 

 but I hope to be able to give a somewhat more complete history 

 of the whole subject than has appeared in any single previous 

 memoir. 



At their first appearance the cells destined to form the per- 

 manent vertebrae present the same segmentation as the muscle- 



1 Das Kopfskdet d. Selachier, p. 123. 



2 Entwicklungsgeschichte d. Unke, pp. 433 4. 



:i Zeitschrift f. Wiss. Anat. Bd. XXV., Supplement. 



