140 THE EMBRYOLOGICAL CRITERION 



horn of the hyoid. The stapes forms a close connection with 

 the hammer and the incus. In birds, where there is a single 

 ear-ossicle, the columella, the middle piece of arch I forms, as 

 we have seen, the quadrate, by means of which the lower jaw 

 is joined to the skull. The proximal end of Meckel's 

 cartilage, which in mammals forms the hammer, here gives 

 the articular surface between the lower jaw and the quadrate. 

 The columella is formed from the middle piece of the three 

 into which the cartilage of the second arch segments. It is, 

 therefore, the homologue of the stapes in mammals. The 

 third arch takes a varying share, together with the second, in 

 the formation of the hyoid apparatus. 



In this paper Reichert made a distinct advance on the 

 previous workers in the same field Rathke, Huschke, von 

 Baer, Martin St Ange, Duges. Huschke was indeed the 

 first to suggest that both upper and lower jaws were formed 

 in the first gill-arch. But both von Baer and Rathke 1 held 

 that the upper jaw developed as a special process independent 

 of the lower jaw rudiment, and the actual proof that the 

 upper jaw is a derivative of the first visceral arch seems to 

 have been first supplied by Reichert. His brilliant work on 

 the development of the ear-ossicles founded what we may 

 justly call the classical theory of their homologies. II is 

 views were attacked and in some points rectified, but the 

 main homologies he established are even now accepted by 

 many, perhaps the majority of morphologists. 



In a paper of 1838 on the comparative embryology of the 

 skull in Amphibia,' 2 Reichert added to his results for mammals 

 and birds an account of the fate of the first and second 

 visceral arches in Anura and Urodela. 



The first visceral arch, he found, gave in Amphibia practi- 

 cally the same structures as in the higher Vertebrates. Its 

 skeleton segmented, as in mammals and birds, into three 

 parts ; the upper part gave rise to the palatine and pterygoid 

 in Anura, but seemed to disappear in Urodeles, where the 

 so-called palatine and ptervgoid developed in the mucous 

 membrane of the mouth; the middle part gave, as in birds, 



1 Ahhandl., i., p. 102, 1832 ; ii., p. 25, 1^33. (R/cnnius pnpcr). 



r,-f^l,-ic/icni/t- Entwickelungsgeschickte iicx Kopfrs tier mickten 

 A)iip/iil>i<'!i } Konigsberg, quarto, 276 pp., 1838. 



