138 THE EMBRYOLOGICAL CRITERION 



history of the cmbryological study of the skull in some 

 detail below ; meantime, we note the two other important 

 lines of research which characterise this period. One is the 

 intensive study of the development of the human embryo, 

 a study pursued by, among others, Pockels, Seiler, Breschet, 

 Velpeau, Bischoff, Weber, Miiller, and Wharton Jones. 1 The 

 other important line - - the early development of the 

 Mammalia was worked chiefly by Valentin,- Coste, 15 and, 

 above all, by Bischoff, whose series of papers 4 was justly 

 recognised as classical. 



What interests us chiefly in the work of this embryological 

 period is, of course, the relation of embryology to comparative 

 anatomy and to pure morphology. The embryologists were 

 not slow to see that their work threw much light upon 

 questions of homology, and upon the problem of the unity 

 of plan. Von Baer, we have seen, recognised this clearly 

 in 1828 ; Rathke, in one of his most brilliant papers, the 

 Anatomisch-philosophische Untersuchungen iibcr den Kiancu- 

 appai-at und das Zungcnbciu (Riga and Dorpat, 1832), 

 used the facts of development with great effect to show 

 the homology of the gill - arches and hyoid throughout 

 the vertebrate series; Johannes Miiller made great use of 

 embryology in his classical }'crglciclicndc Anatomic do- 

 My.vinoiden (i. Theil, 1836), and, according to his pupil 

 Rcichert, firmly held the opinion that embryology was 

 the final court of appeal in disputed points of comparative 

 anatomy ; 5 Reichert himself in a book of 1838 ( Vcrglciclicndc 



1 Kolliker, Entwickelungsgeschichte^ 2nd ed., p. 17, Leip/ig, 1879. 



- I/andbuch dcr Entwickelungsgeschiclite dcs Menschcn nnd . . . dcr 

 Sdugethiere und Vi>cl, Berlin, 1835. 



3 Embryo^c'nic compan'c, 1837 ; Histoirc generate du cUveloppement 

 dcs corps organist's, 1847-49. 



1 Entwickelungsgeschichte des Kaninchen-EieS) Braunschweig, 1842 ; 

 Entwickelungsgeschichte dcs IIunde-Eics, Braunschweig, 1^45 ; Ent- 

 wickelungsgeschichte dcs Meersckweinchens^ (iiessen, 1852; Entwickc- 

 lungsgeschichte des Itches^ (I lessen, 1854. 



" "It is the role of embryology, as my great teacher says, to form 

 the court of appeal for comparative anatomy, and it is from embryology 

 particularly, which has in the last decades provided such signal 

 instances of the unravelling of obscure problems, that \ve have to expect 

 a definite clearing up of the problems relating to the development 

 of the head." Muller's Archiv, p. 121, 1837. 



