The mucous inembrane lining the uterine cavity is composed of the following elements, besides the utricular glands, capillary vessels, and epithelium, viz., — free elementary cor puscles or nuclei, contractile fibre-cells, and amorphous connective tissue.
1. Free elementary corpuscles or nuclei. — These are in all respects precisely similar to the elementary corpuscles already described as constituting apparently the embryonic state of the contractile fibre-cells in the muscular coat. They form in conjunction with the amorphous matter the principal portion of the uterine lining membrane towards its inner surface. Here they are arranged in nearly close apposition, being imbedded in an amor phous blastema, yet not so closely as to cause any mutual disturbance of their round or oval forms.
2. Fusiform fibres or contractile In the account which has been already. given of the muscular coat, the contractile fibres are described as existing in all the coats of the uterus. In the mucous membrane they are very abundant, especially towards the outer surface, or that part in which the mus cular and mucous coats become conjoined, and where the transition from the one to the other is ahnost imperceptible, and is chiefly observable on account of the difference in the arrangement of the constituent tissues of each.
The fusiform fibres of the mucous membrane are gathered into loose bundles, united by amorphous tissue and intermixed with the elementary. corpuscles from which they are developed. These bundles, the form of which is sometimes like the head of an arrow, are usually found between the utricular glands, pointing in a direction perpendicular to the uterine cavity.
The individual fibres have here a softer, paler, and more fleshy aspect than in any other portion of the uterine coats ; they are apparently the youngest and most newly formed of the muscular fibres composing the uterus.
3. Amorphous connective tissue constitutes the chief bond of union between the several elements of the uterine mucous coat, and enters largely into the composition of the utricular glands. It presents no special cha racter requiring a more particular description than has been already. given of it in the ac count of the muscular coat.
Utricular glands or follicles. — These struc tures, which were first more particularly described by E. II. Weber and Professor Sharpey, constitute the most remarkable cha racteristic of the uterine mucous membrane.
By Reichert*, who has also investigated the subject, they were found present in every mammal which he had examined. The ute rine glands or follicles consist of involutions or depressions of the mucous membrane, which are exceedingly numerous, and lie tolerably close together. They generally present the forua of canals taking their course from the muscular walls of the uterus, through the sub stance of tne parenchyma of the mucous membrane towards its free surface, where they terminate each in a separate orifice.
In Ruminantia and Pachydermata they are large, and take a serpentine direction, so that they may be easily mistaken for vessels. By Burckhardt indeed, who has described them in the cow, they were termed vasa spiralia. Their spiral course is more obvious in the rodentia and carnivora. In the rabbit they are short and wide. The orifices by which the utricular glands terminate upon the surface of the mucous membrane are in some ani mals large enough to be distinguished by the naked eye, as, for example, in ruminants, and occasionally in man ; but more frequently' these require the aid of a lens fbr their detection.
In the dog, two sorts of glands are de scribed by Professor Sharpey simple and compound. The simple glands, which are the more numerous, are merely very short unbranched tubes closed at one end ; the compound glands have a long duct dividing into convoluted branches ; both open on the inner surface of the membrane by small round orifices, lined with epithelium, and set closely together.
In man the form of the uterine follicles is by no means so definite as in the dog ; nor is it possible by any mode of dissection with which I ain acquainted to isolate and display them separately.* They form in fact a sys tem of tortuous canals ramifying in the sub stance of the mucous membrane, in which they seem as it were to be excavated. They are so closely set as apparently to possess no distinct boundary wall, but each canal is sepa rated from those contiguous to it by a variable thickness of parenchyma, consisting chiefly of the elementary corpuscles and amorphous tis sue just described, together with a certain ad mixture of fibre-cells, usually found near the basal ends of the glands. No section that I have ever made has succeeded in exhibiting even a single gland divided longitudinally in such a way as to lay open the canal in its entire length, but every section made per pendicular to the surface presents the same appearance of numerous close-set meandering canals laid open for short distances, and giving to the surfaces of the section an outline whether by any indirect communication with the uterine vessels, w hich many considerations both physiological and pathological seem to point out as at least possible. The difficulties attending this part ot the enquiry have been ably illustrated by Dr. Sharpey, and my own investiptions fully confirm his statements upon this point. Nevertheless I have in many in stances succeeded in distinctly observing, the blind termination of these canals towards the muscular coat.* When sections of the mucous membrane are made parallel with, instead of perpendicular to, the surface, these canals are seen divided across. The appearance then presented is that of numerous round or oval apertures, which are more distinct in proportion as the section is made nearer to the uterine cavity.