582 THE PHYSIOLOGY OF REPRODUCTION 



The placental area at the end of parturition is marked by the 

 presence of thrombosed vessels. It is raised above the general 

 surface of the uteri>ne wall, and is irregular in shape. It very soon 

 diminishes in size, its diameter being not more than two centimetres 

 long at the end of the puerperal period, although its former position 

 may be detected as an area slightly stained by blood pigment for 

 several months after delivery. 



Williams states that in the last month of pregnancy some of the 

 sinuses at the placental area imdergo thrombosis, but that this 

 process becomes much more marked after the completion of labour, 

 although many of the sinuses are simply compressed by the contract- 

 ing uterine muscles withoiit ever becoming thrombosed.^ The 

 thrombi are eventually converted into ordinary connective tissue 

 by a cellular prohf oration from the lining membrane of the vessel.s 

 While this change is in progress the lining membrane presents a 

 folded appearance somewhat resembling a typical developing corpus 

 Iviteum. This is especially well seen about the fourth week after 

 parturition, but even up to the end of a year the convoluted appear- 

 ance is "still sometimes discernible.^ The lumina of the arteries become 

 reduced in size, but the thickening of their walls, which takes place 

 during pregnancy, is an alteration of a more permanent character. 

 This histological change affords a means of discriminating between 

 a virgin and a parous uterus. 



Leo Loeb and Huramitau^^have studied the involution of the 

 uterus in the guinea-pig and find that it is favoured by suckling. 

 They regard the effect on the uterine tissues as acting directly, and 

 not indirectly by way of the ovaries. Castration is stated to favour 

 uterine involution in the guinea-pig. 



The human cervix remains for some time after delivery as a soft 

 flaccid structure with lacerated edges, but it gradually undergoes 

 involution, the lumen becoming narrower. The vagina takes about 

 the same time to recover as the uterus. After a first delivery its 

 outlet remains permanently wider than before. The rugae reappear 

 about the third week. The place of the hymen is taken by numerous 

 small tags of tissue which become transformed into the carunculse 

 myrtiformes. The condition of the labia majora and labia minora is 

 generally flabby and atrophic as' contrasted with that existing in 

 virgin women. 



' According to Longridge (see below in the text), thrombosis is of little or 

 no importance in assisting the haemostasis of normal labour. 



^ Williams (Sir J.), " Changes in the Uterus, etc.," Trans. Obstet. Soc, vol. xx., 

 1878. See also Helme, " Histological Observations, etc.," Trans. Roy. Soc. Edin., 

 vol. XXXV., 1890. 



' Huramitau and Leo Loeb, "The Involution of the Uterus following 

 Labour," Amer. Jour. Physiol., vol. Iv., 1921. 



