OBSERVATIONS ON THE HISTOLOGY 



AND PHYSIOLOGY OF THE PLACENTA 



OF THE MOUSE 



J. W. JENKINSON ffl. A., 



Assistant to the Linacre Professor of Comparative Anatomy in the University of Oxford. 

 With PI. IV-VI. 



INTRODUCTION. 



It is now eleven years since Professor Mathias Duval published 

 in his 'Placenta des Rongeurs', a full account of the placentation 

 of the mouse. His paper was published almost simultaneously with 

 Hubrecht's memoir on Erinaceus, and in it he showed conclusi- 

 vely that the placenta was essentially formed from a tissue of 

 embryonic origin, the 'ectoplacenta'. 



After describing the manner in which the embryo becomes 

 fixed in an anti-mesometric pit or crypt, (with concomitant dis- 

 appearance of the uterine epithelium) Duval divided the whole 

 process of placentation into the three periods of 'formation', 

 'remanieinent', and 'achèvement' of the 'ectoplacenta'. 



Putting aside the history of that portion of the ectoplacenta 

 which is adjacent to the distal wall of the invaginated yolk-sac, 

 the formation of the new lurnen of the uterus on the anti-meso- 

 metric side of the embryo, and the ultimate disappearance of all 

 the maternal and foetal tissues in this region (with the exception 



