310 DR A. MILNES MARSHALL. 



of appearance of the olfactory lobe is the point in which 

 there is the greatest discrepancy between the descriptions of 

 previous writers and my own, I have made sections in very 

 various ])lanes in order to detect any appearance that could 

 possibly be interpreted as an olfactory lobe at an earlier date 

 than the seventh day, but have failed completely to observe 

 any such. 



As far as I can ascertain, the earliest account of the deve- 

 lopment of the olfactory nerve is that given by Remak ; this 

 description, which only occupies about three lines, and is unsup- 

 ported by figures, is as follows : — " An ihrem Boden (Hemis- 

 pharen) zeigen sich gegendas Ende des drittenTages jederseits 

 kleine birnformige Blaschen (Geruchsblaschen) iiber deren 

 weiter entwickelung ich keine Beobachtungen besitze."' This 

 observation was repeated later on by von Baer, who, however, 

 went further than Remak, and described this vesicle as the 

 rudiment of the olfactory nerve ; he also described an olfactory 

 pit distinct from this vesicle. Concerning these statements 

 Remak speaks thus : — " Halte ich diese Angaben mit meineu 

 eigenen Wahrnehmungen zusaminen, so wird es mir sehr 

 wahrscheinlich, dass Baer am vierten Tage die Geruchs- 

 blaschen und die Nasengruben nicht gleichzeitigbeobachtet, 

 dass er vielmehr dasselbe Gebilde bald als Anlage des 

 Riechnerven, bald als Nasengrube gedeutet hat. Ich habe 

 mich namlich iiberzeugt, dass die Geruchsblaschen, die zu 

 Ende des dritten Tages auftreten, die nasengruben sind, und 

 dass weder alsdann, noch bis zum fiiiiften Tagen ein entspre- 

 chender Auswuchs des vorderhirnes wahrzunehmen ist."^ 

 This very definite statement shows with perfect clearness 

 not only that Remak recognised and corrected his original 

 mistake, recognised, i. e. that what he had originally taken 

 for outgrowths of the cerebral hemispheres were really the 

 olfactory pits, a mistake doubtless due to his relying on 

 surface view of whole embryos; but also that he discovered 

 and recorded the fact that as late as the end of the fifth 

 day there is no trace of an olfactory lobe. 



Strange as it may seem, this exceedingly definite and 

 accurate statement of Remak's has been completely over- 

 looked, while his earlier, vague, brief, and avowedly imper- 

 fect observation actually furnishes the basis of the descrip- 

 tions of the development of the olfactory nerve given in our 

 text-books of embryology at the present day. 



Thus, Professor Kolliker, in the second part of his text- 



* ' Untersuchungen iiber die Entwickelung der WiibeltLiere.' Berlin, 

 1855, p. 33. 

 2 Log. cit., p. 74, note 55. 



