UTERUS (DEVELOPMENT). 



any substance within the uterus, such as a 

 polypus, which may cause distension of its 

 walls ; or by the accumulation of fluid in its 

 cavity, such as the menstrual fluid collected 

 in cases of atresia or impsrforation of the 

 vagina. 



The development of the uterus which is 

 occasioned by the stimulus of pregnancy, takes 

 place whether the impregnated ovum arrives 

 within the uterine cavity or not ; although 

 this does not occur in equal degrees in the 

 two cases. In the case of extra-uterine preg- 

 nancy, a very considerable thickening of the 

 uterine substance usually takes place, together 

 with a general enlargement of the entire organ, 

 fully equal to that which is observed in the third 

 month, and, in some cases, when gestation is 

 not interrupted, even in the fourth month of 

 ordinary pregnancy. 



In cases where gestation follows an ordi- 

 nary course, the development of the uterus is 

 such, that the weight, at the end of the period, 

 is found to be increased about twenty-four- 

 fold, and its length about five-fold. 



This development, as it affects the size, 

 weight, form, and position of the entire organ, 

 as well as the physical condition of its special 

 parts, will now be considered. 



There is no example in man, and few in the 

 animal kingdom generally, of a development 

 of any organ or structure comparable in rapi- 

 dity with that which takes place in the uterus 

 during gestation, although the periodical 

 growth of the deer's horn, and the formaiion 

 of the placenta, may be quoted as in some 

 respects analogous cases. 



Size. The rate of increase of the uterus, 

 during pregnancy, is subject to great varia- 

 tions. But, with due allowance for these, 

 which are dependent chiefly upon the size of 

 the foetus and placenta, the quantity of liquor 

 amnii, or the number of ova fertilised, an 

 approximate estimate may be formed of the 

 average alterations in size and bulk which the 

 organ exhibits at different periods of normal 

 gestation. 



These may be expressed in calendar months 

 as follows : 



RATE OF INCREASE IS SIZE OF THE GRAVID 

 UTERUS ACCORDING TO MONTHS. 



The antero-posterior has usually an average 

 of one inch less than the lateral diameter. 



Weight. The weight of the gravid uterus, 

 when fully developed, is most correctly ascer- 

 tained in cases where death has taken place 

 during, or soon after, labour at term. In 

 twelve examples, estimated by Meckel, the 



645 



minimum weight was 2lbs., and the weight, 

 relatively to the unimpregnated organ, was 

 as 2-4 to' 1.* 



Form. The form of the uterus undergoes 

 many changes in the course of gestation. 

 During the first three months, although there 

 is a considerable increase of size, the primitive 

 figure is retained with only slight alterations. 

 After the third month, the body rapidly en- 

 larging, while the cervix remains nearly un- 

 altered, the figure of the former approaches 

 that of a sphere. For the perpendicular and 

 transverse diameters of the body then become 

 nearly equal, and the only deviation from the 

 spherical form is occasioned, first, by the 

 cervix, which increases the vertical dia- 

 meter of the entire organ by one inch ; and 

 secondly, by the more tardy expansion of the 

 body in the antero-posterior diameter, pro- 

 ducing the form of a flattened sphere. After 

 this, the perpendicular increasing more rapidly 

 than the transverse diameter, and the upper 

 segments widening faster than the lower ones, 

 the uterus gradually acquires the ovoid figure 

 which characterises it at the end of pregnancy. 



Alterations, nearly corresponding with these, 

 take place in the cavity of the uterine body. 

 The walls of this flattened triangular chamber 

 begin to separate from each other ; and by 

 their gradual expansion,, the angles and supe- 

 rior and lateral lines, by which the cavity was 

 at first bounded, are unfolded, so that the tri- 

 angular is gradually exchanged for the pyri- 

 form shape, and this again for the figure of a 

 flattened sphere as in the fourth and fifth 

 months of gestation ; after which period the 

 figure of the cavity corresponds very accu- 

 rately with the general external form of the 

 organ. 



During these alterations, the fundus be- 

 comes strongly arched; while the sides un- 

 dergo a slighter relative expansion, so that 

 they exhibit only a gentle swelling ; but the 

 anterior and posterior walls become curved 

 and prominent sometimes the former, and 

 sometimes the latter, according to Dr. W. 

 Hunter, showing the greater amount of con- 

 vexity.f 



It has often been asked whether, during 

 these changes, the walls of the uterus increase 

 in thickness, or the contrary. In other words, 

 whether the dilatation of the uterine cavity is 

 to be regarded as a mere passive distension, 

 with thinning of the walls; or whether the 

 process of enlargement consists of an active 

 excentric hypertrophy. 



In order to determine this point, Meckel 

 examined the average thickness of the uterine 

 walls at different periods of gestation. From 

 observations which he had made in sixteen 

 uteri, at all periods of gestation, he concluded 

 that the walls increase a little in thickness in 

 the beginning, but that this increase is not 

 very considerable, and that towards the end 

 of pregnancy they become gradually much 



* The estimates of Heschl, given at page 658., 

 differ somewhat from these. 



f W. Hunter. An anatomical description of the 

 human gravid uterus, page 5. 



T T 3 



