In order to determine this point, Meckel examined the average thickness of the uterine walls at. different periods of gestation. From observations which lie 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 thinner. He found the thickness of the rine walls, three weeks after conception, 6"'; During these changes, which take place in the uterine body in the course of pregnancy, similar, but much slighter, alterations occur in the cervix. For the latter, being only the ex cretory channel of the uterus, undergoes no further modification than is necessary to pre pare it for transmitting the foetus %hen fully developed. Accordingly, in the early months of gestation, while the body is rapidly en larging, the cervix undergoes but little change. Its tissues, however, become slightly expanded, so that the whole part is thicker, softer, and more elastic than in the virg,in state. The margins of the os extern= are consequently rendered more cushiony, and the orifice itself is enlarged. The canal of the cervix is also widened, and the palmm plicatm become un folded, and project in the form of frill-like expansions crag. 416.); while an unusual ac tivity, occurring- in the crypts and follicles, by which these parts are covered, a tough gelatinous secretion is poured out, which at the commencement of the third month, 5"/ ; at the commencement of the fourth month, 4m. At the end of the fourth month, in two cases, 4"'; in a third, 3"/ at the upper, and 4"' at the lower part ; in a fourth, 5"'. At five months, in one case, 3"'; in another, 2" superiorly, and 4"' inferiorly. At six and seven months, rather less than 3'" ; at eight months, in one case, 2"', and 23/4"' ; and in another, 3"' above, and more than 4"' below. At nine months, they appear to be still rather thinner.
In several uteri, which I have examined at all stages of gestation, I have found the thick ness of the uterine walls exceedingly variable in different instances, even at corresponding periods of pregnancy', and particularly variable also in different parts of the same uterus.* According to my measurements, the extremes of' thickness range from 2"/ to 9'".
• This circumstance is remarkably exemplified in prep. No. 3605, in the Museum of the Royal College of Surgeons, London.
collecting here in the form of a plug, assists in shutting out the uterine cavity and its contents from contact of external air and other influences.
The increase in size of the os and cervix, which is gradually progressive through the whole of gestation, will be sufficiently ex pressed by comparing the dimensions of these parts in their two extreme states. The virgin cervix measures usually at the base 7-8"' in its shorter, and 11-12"' in its transverse dia meter, and has an aperture of 3-4"' wide. It projects into the vagina to the extent of 4'" (fig. 425). At the end of pregnancy, the whole vaginal portion of the cervix would fill a circle of 1 f" diameter ; the orifice measures transversely 10 1 ; and that part which formerly projected into the fornix of the vagina, is now reduced nearly to the level of the vaginal walls.
During these changes, it is often observed, especially in a first pregnancy, that, RS gesta tion advances, the projection of the cervix uteri into the upper part of the var,ina be conies gradually less and less distinctry ascer tainable by the finger. The latter change is commonly- termed the " shortening of the cer vix ;" but the conditions upon which it de pends, have not been very accurately examined, and they are certainly not at all clearly or adequately represented by the figures by which the description of this process is usu ally accompanied. As much importance is usually attached, in works on forensic and obstetric niedicine, to the changes in question, it will be necessary here to examine a little more closely the process by which this appa rent shortening of the cervix is produced.
It is commonly said that no material altera tion, in the length of the cervix uteri, occurs before the fifth month of gestation ; that, at the sixth or seventh month, the uterine neck has begun to shorten ; at the 'eighth month, it is nearly, and at the end of the ninth month, it is quite, obliterated.
But while it is true that a lessening of the projection of the cervix into the vagina com monly takes place in pregnancy (fig. 446.), I can hardly coincide in the explanation which is usually offered of this circumstance, namelb that it is due to a gradual drawing up, as It were, of the cervix, by which its walls become added to those of the body of the uterus, for the purpose of increasing the capacity of the uterine cavity ; and that in this way the ute ine neck is gradually shortened, until it finally disappears.* The accompanying fig. 446. exhibits the condition of the cervix in a woman aged thirty-seven, who, having previously borne children, died of phthisis in the eighth month of pregnancy-. Here it will be perceived, that, without any actual diminution of the length of the cervix, which measured rather more than one inch, still there is no projection of it into the vagina ; but that it forms a flat roof to that canal in the mode which is usually described and explained as indicatino. the en tire absorption of the uterine neck. °The true explanation of this, as it appears to me, is, that the apparent shortening of the neck is caused not, at first, by any diminution of its actual length, but by an increase of its breadt h, or its extension in the lateral direction, where by the projection of the lips into the vagina is reduced to the smallest possible amount. The rest of the process, upon which the shorten ing of the cervix depends, may be explained See description of the figures in Gooch : "An acconnt of some of the most important diseases peculiar to woman," p. 212; and Beck's Elements of Medical Jurisprudence, 5th edit. p. 128.