A second view is obtained by cutting com pletely through the uterus in the direction of its transverse diameter, and parallel with its extremities. If the entire organ be cut up into many such segments (fig. 427-430.), itis then seen, from the length of the central line, that the cavity varies in breadth, its widest part being in the segment which includes the ex tremities of the Fallopian tubes ; whilst from this point downwards the line diminishes in length, until at the narrowest portion of the uterus, or that representing the commence ment of the cervix, it measures only 1r 3"' in diameter.
But the most complete view of the interior of the uterus is obtained by a section carried through the centre of the organ, dividing it midway between its anterior and posterior walls. The entire cavity which is thus ex hibited at one view is seen to be of a trian gular form ; its boundaries being formed superiorly by the fundus, and on either side by the two lateral borders, whilst in each angle is observed an aperture. The two su perior openings are the lower orifices of the Fallopian tubes. The inferior opening lead ing to the cervical canal constitutes the os uteri internum (fig. 431. i).
Since the cavity in the interior of the uterine body has a triangular form, whilst externally the shape of the organ is rnore or less pyriforrn, it is evident that the parietes of this " hollow muscle " cannot have every where an equal thickness, for otherwise the form of the cavity would correspond with that of the external surface. But whilst the anterior and posterior walls exhibit an average and nearly uniform thickness of about 6'", that of the lateral boundaries and of the fundus varies from 6'" to V". Hence the section of this cavity represented in fig. 426., which exhibits the organ as divided from before backwards, is described by a right line ; whilst the section (fig. 431.) sh-ows the cavity as bounded by' three curves, the degree of curvature vary ing in different subjects, and being generally supposed to be always greatest and most marked in women who have never borne children.
This point has been much dwelt upon as serving to distinguish the nulliparons from the multiparous uterus. I have reason to think, however, that this observation has been again and again repeated without con firmation by an appeal to facts. For although the sides of the virgin uterus are often strongly incurved, yet in some uteri in my possession from young subjects who had not borne children, the walls of the cavity are nearly straight, and this is the form which they have in the fcetus (fig. 442.), and in undeveloped
uteri (fig. 465.); whilst in other specimens, taken from women who had borne many chil dren, the sides and fundus may be incurved in various degrees. Much will depend upon the mode in which the sections are rnade; for un less, in dividing the organ, the knife has passed exactly through the median line, a portion of either the anterior or posterior wall will be in cluded in the section, and the apparent form of the cavity will be materially modified thereby.
Thus the uterine cavity in the unimpreg nated state is nothing more than the narrow interspace between the flattened walls which are normally either in immediate contact, or are separated from each other by only a small quantity of mucus. The triangular form re sults from the confluence of three ducts or channels ; viz., the two oviducts above, and the cervical canal below. The tubal canals, having passed through the substance of the uterus, expand trumpet-like into the uterine cavity, whilst in the same way the cervical canal traced upwards is prolonged, though more gradually, into the same cavity. But the perpendicular diameter of the uterus being always greater than the transverse, the form of the cavity, in so far as it is trian gular, represents not an equilateral, but an isosceles triangle with incurved sides (fig. 431.).
By reference to these particulars regarding the form of the interspace between the uterine walls, we are enabled to explain many pheno mena relating to the first entrance of the ovuin into the uterus, and its mode of' deten tion there, before it has become organically united to the uterine walls.
The cavity of the uterus is lined by a mu cous membrane, the peculiarities of which will be afterwards more fully described. This membrane appears to the unaided eye nearly. smooth, and is usually of' a pale pink colour, except in those cases where death has oc curred during menstruation, when it is of a deep red hue, and more or less plainly vasctilar. A moderate amplify log power, however, suffices to show that the mucous membrane is not smooth, but is perforated everywhere by minute apertures, yvhich are the orifices of numerous ramified canals or follicles occupying the substance of the mu cous membrane, and lying for the most part in a direction perpendicular to the surface upon which they terminate. A few folds are occasionally' perceptible in the mucous mem brane, these being seen chiefly in the neigh bourhood of the tubal orifices.