External to and surrounding these may be distinguished a second order of strata, among which the primary and secondary ramifica tions of the principal uterine arteries and veins are freely distributed ; so that sections taken from this region do not present the same compact appearance as those from the inner layers, but are seen to be everywhere per meated by vascular channels, which are par ticularly conspicuous in the multiparous uterus. These numerous vessels, ramifying among the muscular fibres, make the course of the latter very irregular. When the section has been made parallel with the broad liga ment, the tortuous arteries, entering the uterine texture between the folds of the lat ter, may be often traced to a considerable depth among the Latham ; while sections made in an opposite direction more frequently exhibit the gaping orifices of these vessels, and of the divided veins surrounded by lami nm of muscular fibres, and of a more lax and fibrillated form of connective tissue, than is found among the inner strata. This inter mixture of the larger uterine vessels with the muscular strata constitutes here a very cha racteristic feature, and hence these middle strata may be distinguished as the vascular laminm of the muscular coat.
External to these again lie a series of thin sheet-like laminm (fig. 437.), forming a tegu mental stratum which does not entirely sur round the organ, nor cover it in all its parts. It consists of 6-12 thin close-lying layers of fibres, whose course is parallel with the uterine surface ; the most external laminm being inseparable from the peritoneum by which they are covered. These flat, thin, layers are continuous with and extended upon and into the broad and round lig,aments, the Fallopian tubes, and the lig-aments of the ovary, from which they spread out fan-shaped over the fundus and upper portion of the anterior and posterior uterine walls ; meeting at length in a central perpendicular raphe, in which a few longitudinal bundles may be generally seen.
These tegumental laminm are composed almost entirely of fusiform fibres, with very few embryonic corpuscles. They are united together by a large proportion of strongly fibrillated connective tissue, which is, how ever, sufficiently lax to permit a certain amount of artificial separation of the laminm.
Within these laminm the fibre-cells are arranged in a manner somewhat different from that which characterises the internal strata. The amount of amorphous connecting matrix is here so sinall that the fibre-cells lie ap parently in close apposition, their extremities interdigitating with each other, so as to form an imbricated pattern (fig. 43 I..). These fibres do not so frequently change their course as the fibres of the innermost strata, but form a more continuous series ; so that sections of this part of the muscular coat are easily ob tained, exhibiting the appearance of longitu dinal strata, or bundles of fibre, such as are represented in fig. 437. The course of the individual fibres within them is, however, traced with difficulty, on account of the large quantity of fibrillated connective tissue by which these layers are surrounded and con joined.
Immediately beneath the peritoneum all the constituents of the muscular coat are con densed into a tissue which cannot be easily unravelled. Through this, however, nume rous fibres may be seen to run in a direction more or less perpendicular to the surface, apparently for the purpose of connecting the peritoneum with the coat beneath.
The mucous or deciduous coat ; Lining mem brane of the cavity if the uterus.—Thib forins a moderately thick and soft layer which lines the entire cavity of the uterus, and is con tinuous with the lining membrane of the Fallopian tubes, and of the cervical canal. On account of the large supply of capillary vessels which it receives, the mucous mem brane is usually distinguished from the rest of the uterine parietes by its brig,hter red colour. It pre.sents also to the unaided eye, when horizontal sections are examined, an appear ance of being thrown into minute folds run ning perpendicular to the uterine cavity (fig. 438.). These apparent foldings, however, are shown by a strong lens to consist of a series of ramified canals, which constitute the most remarkable peculiarity of this meni brane. The proportionate thickness of the mucous membrane relatively to the rest of the uterine walls, though variable in respect of age and other circumstances, is usually about ith of their diameter. Its greatest thickness is found about the middle of the cavity, while towards the internal os uteri, and still more in the region of the fundus, the thickness is slightly diminished.
To the unaided eye, the. mucous membrane lining the body of the uterus, when viewed from the uterine cavity, is apparently smooth, or is seen to be perforated by minute aper tures, but it rarely presents the appearance of deep folds or plicm such as are alway s found in the cavity of the cervix. Occasion ally the surface is roughened and floculent from the exfoliation of its epithelial cover ing. The appearance of minute perforations is then lost, and a tomentose or apparently villous condition of the surface occasioned by the loosening out and partial detach ment of the capillaries which freely ramify within this membrane is observed, The lining membrane of the uterus differs from mucous membranes in general in hav ing no sub-mucous tissue, .so that it can not, like that ot the intestines, be made to glide upon the sublying tissues, nor be dis sected off from them so as to be displayed in a distinct layer. When very thin sections from spirit preparations are examined by transmitted li,ght with a common lens, or vvith a low power of the microscope, the mu cous is distinguishable from the muscular coat chiefly by its greater opacity and peculiar greyish colour, as well as by the numerous tortuous canals which permeate its substance, running chiefly in a direction perpendicular to the inner surface of the membrane, and strongly resembling in their general contour the cerebral convolutions Under the application of dilute acetic acid this comparative opacity' and grey hue imme diately disappear, and the tortuous canals alone serve to mark the boundary between the two coats. When an amplifling power sufficient to discriminate the component tis sues is employed, the distinction between the two coats becomes still less apparent, because their constituent elements are then seen to pass fi out the one to the other by almost itn perceptible gradations, the difference between them being then shown to be morphological rather than structural, at least, at the points of their confluence.