776 



A TEXTBOOK OF PHYSIOLOGY 



labour is not known. The process is normally reflexly controlled 

 through a centre in the lumbar cord, although the presence of this 

 centre has been shown not to be necessary. At term the uterus is 



,0CIOUA VEPA 



3UA RETLECTA 

 ,DE.CIDUA 6ASAUIS 



DECIOL 



A\ BLASTODERMlC 

 u* \ VESICLE 



DEC'DUA VE&A 



DECIDUA VERA 



VAGINA 



FIG. 483. SECTION* OF UTERUS SHOWING IN DIAGRAMMATIC MANNER THE EMBEDDED 

 OVUM AND THE DIFFERENTIATION OF THE DECIDE INTO THREE PARTS. (Keith.) 



uterine vessel- 



submuc layer^ 

 of uterus 



decidua- 



synoytium 



sgncytium. 

 basal layer. 



mesoblast 

 of chorion 



uilfus/ 



blood sp'ace 



FIG. 484. DIAGRAMMATIC SECTION OF THE DECIDUA SEROTINA (FORMED FROM 

 THE Mucous MEMBRANE OF THE UTERUS) AND CHORION TO SHOW THE MANNER 



IN WHICH THE PLACENTAL BLOOD SPACES ARE FORMED. (Keith.) 



of large size, reaching high up into the abdomen. After delivery by 

 the process of " involution," it returns again within the pelvic cavity. 

 The involution is said to be due to the autolytic action of intracellular 



