UTERUS (DEVELOPMENT). 



small size and dimensions characteristic of the 

 virgin state. 



Metamorphosis and restoration of the com- 

 ponent tissues. The first and immediate re- 

 duction in size of the uterus, after parturition, 

 has been just stated to depend upon mere 

 contraction of the uterine fibre. But con- 

 traction alone will not account for those great 

 and remarkable reductions in the dimensions 

 of the organ which have been just described. 

 The true explanation of these phenomena is 

 furnished by a series of metamorphoses affect- 

 ing more or less the entire uterine tissues, by 

 which the greater portion of those structures 

 which have been formed during pregnancy, 

 become disintegrated and removed, while 

 other and new tissues are developed in their 

 place.* 



In these metamorphoses, the colossal fibre 

 cells, which form the great bulk of the newly 

 added material, play the most important part. 

 These have been traced, during their develop- 

 ment in pregnancy, from the small fusiform 

 cell of the unimpregnated uterus to the fully 

 formed fibre of the organ at term. The growth 

 of these proceeds pan passu with that of the 

 foetus, for whose expulsion they are destined ; 

 and this act being accomplished, their de- 

 struction and removal becomes a necessary 

 prelude to the recomposition of the entire 

 organ upon the same type as before impreg- 

 nation. In this respect, the aggregate forma- 

 tion of fibre cell is comparable to the deer's 

 horn, the placenta and other structures which, 

 having served the purpose of their formation, 

 and being incapable of .suffering retrogression, 

 become caducous, with this difference, how- 

 ever, that the one class of structure being 

 thrown oft' in a mass, the act of separation is 

 striking and obvious ; while the deciduous 

 process in the other is gradual and fragmental, 

 and can only be discovered by the most pa- 

 tient and careful scrutiny. 



The disintegration and removal of the ute- 

 rine muscular fibre is effected, first, by the 

 transformation of each fibre into molecular 

 fat. This process does not commence earlier 

 than the fourth or sixth day after labour, and 

 not later than the eighth day. Certain dif- 

 ferences are observable in the order of retro- 

 gression. Thus the process begins somewhat 

 later in the inner than in the outer laminse, 

 while the cervix remains unchanged a few 

 days longer than the body. In the individual 

 fibres, the process of decay begins at many 

 points simultaneously. The fibres lose their 

 sinuous outline, and become paler; while 

 within them appear yellow oil granules, 

 commonly arranged in rows. The nucleus of 

 the fibre is pale, but distinct, until it becomes 

 obscured by the increase of the oil granules ; 

 while the extremities of the cells, on account 



* On this subject the following may be consulted 

 with advantage : Dr. R. Heschl, " Untersuchun- 

 gen iiber das Verhalten cles menschlichen Uterus 

 nach der Geburt," in the Zeitschrift der kais. kon. 

 Gesellschaft der Aerzte zu Wien. 1852. B. ii'. 

 p. 228. ; F. M. Kilian, " Die Structur des Uterus bei 

 Thieren," foe. cit. ; Schroeder van der Kolk, foe, cit. 



659 



of their tenuity, are the first to suffer disin- 

 tegration. 



Fig. 455. 



Process of involution or disintegration, and renewal of 

 the uterine fibre after parturition. (After Heschl.) 



a, the old fibres filled with fat granulations 

 2 4 weeks after delivery; b, development of 

 new fibres in different stages, about the fourth 

 week. 



During the second and third week, the 

 process of disintegration continues ; and it is 

 probable that a considerable absorption of 

 effete material now takes place, since it is not 

 easy to explain otherwise that rapid diminu- 

 tion in bulk, especially in the second week, 

 which the entire organ undergoes, as shown 

 by the calculation of weights already given. 

 As a result of these molecular changes, the 

 uterus now loses its reddish colour, and be- 

 comes of a dirty yellow, and is at the same 

 time more easily lacerable. 



In the course of the fourth week, and pos- 

 sibly sometimes during the third, there ap- 

 pears, in the midst of the now degenerated 

 fibres, the first traces of a new formation of 

 uterine substance. These occur first in the 

 form of cell nuclei, which are concurrently 

 developed at several points; and gradually, 

 while the last portions of the old muscular 

 coat are being disintegrated and absorbed, 

 acquire the character of the new muscular 

 fibre cells (fig. 455. b). So that, by the end 

 of the second month, the reconstruction of this 

 portion of the uterine substance is often com- 

 plete. 



The disintegration of the remains of the 

 decidua, and the reconstruction of the limn" 

 membrane of the uterus, which had been re 

 moved during the act of birth, is effected by a 

 process very similar to that just described. 



With regard, first, to that portion of the 

 inner uterine superficies, which had been co- 

 vered by the placenta, it is observed that this 

 undergoes a somewhat slow retrogression. 

 The veins, filled by thick clots in the normal 

 state in consequence of the progressive invo- 

 lution of the intermediate uterine substance, 

 occasion here a marked protrusion ; so that 

 very often, after four or six weeks, the pla- 

 cental space forms an elevated spot of twice 

 u u 2 



