Without entering upon the question of the number of lantinx into which the walls of a Graafian follicle may be split by skilful mani pulation, it will suffice to consider those only as distinct membranes or coats, which exhi bit obvious differences of structure and rela tionship, during the various phases of develop ment and decay which the follicle undergoes from its first formation to its final disappear ance. In this view the walls of the Graafian follicle must be regarded as being composed of three membianes ; and indeed but for the importance attached to the use of the third or innermost of these, which in any case is hardly niore than a thin layer of granules, it would have sufficed if the coats of the vesicles had been enumerated as two only.
The external fibrous or vascular coat (fig. 374. a, fig. 371. E) constitutes the tunic of the ovisac of Barry, the tunica fibrosa, S. theca of Baer. It forms no portion of the ori ginal ovisac, but is a superadded part, derived from the parenchyma of the ovary. This coat closely embraces the ovisac, and partakes in its spherical figure ; it carries numerous blood-vessels, which pass from the ovarian stroma to become expanded in a vascular net work over its Ni alls (fig. 371. u).
Examined by the microscope, this membrane is seen to be highly vascular. It is composed of a fine membrane, containing few fibres, but everywhere abundantly studded with oval nuclei, visible without the aid of acetic acid, and probably, in part at least, due to the pre sence of so many blood-vessels in its tissue. This coat contains no oil globules. Its chief use appears to be to give increased support and protection to the true ovisae which it sur rounds, and to convey blood-vessels from the ovary for its nutrition, and for the supply of the fluids which the ovisac contains.
The second or internal coat, as it is com monly termed, of the Graafian follicle is the ovisac itself. It constitutes at first an inde pendent structure; but receiving afterwards the before mentioned investment from the ovarian parenchyma, the two coats unite to form the Graafian follicle. The ovisac is composed of embryonic fibres of connective tissue (fig. 375. a), of rounded cells or granules, b; and of a large proportion of minute oil globules, c. The embryonic fibre-cells lie parallel with each other, and together with the granules form the bulk of the tissue in nearly equal proportions. The oil drops are very numerous ; and after the preparation has been under examination for some time they are seen to float up to the surface of the drop of water in which it is placed, and to collect upon the under side of the glass disc used for covering it. In addition to these there is found a small quan tity of developed fibres of connective tissue, which appear to give finnness to the whole. The Graafian follicle thus composed, contains, in close contact with its inner wall, a stratum of nucleated cells, forming tin epithelial lining, termed the menzbrana granulosa (fig. 374. c, flg. 371. G). The cells or granules which give a name to this membrane are so lightly held to gether that it has been doubted w hether the stra tum which they form is really entitled to the denomination of a membrane. Nevertheless this
structure appears to play an important part in regard to the ovum, which. is always found lodged within a portion of it. At the com mencement of the formation of the ovisac, ac cording to Dr. Martin Barry,_these peculiar elliptical nucleated cells or granules are nearly equally difised through the fluid which it con tains,, the ovum lying in their centre. But about the time at which the ovisac unites with its covering or tunic to form the Graafian fol licle, these granules are found to have become -separated into little groups, leaving interspaces filled by fluid. Further, as this separation ad vances, the granules arrange themselves in such a manner as to constitute three distinct struc tures. The principal portion collects upon the inner surface of the ovisac forming the vzem brava granulosa just described (fig. 374. c). A second portion becomes aggregated upon and around the ovum, taking its form and constituting a special investment for it. This is the tunica granulosa of Barry (fig. 374. e). A third portion collects to form a structure composed of a central mass in which the ovum with its tunica granulosa is imbedded, corresponding with the cumulus (fig. 371. n,u) of Baer, and of certain cords or flattened bands, from two to four in number, which pass off from the central mass outwards, to become united with the layer of granules lining the follicle. These radiating bands or cords are tertned by Barry the retinacula, (fig. 374. d (1) from their supposed office in suspending the ovum, and retaining it in its proper situation in the Graafian follicle.
That the retinacala, however, are not essen tial structures is proved by the fact that they are wanting in many of the Marnmalia as well as in Man. They have been observed chiefly in the Rodentia and Ruminantia, where their form and number are subject to considerable varia tion. The subjoined figure exhibits the ovum ducted to the lower border of the ovary be tween the folds of the posterior duplicature of the broad ligament, vvhere they lie in parallel lines, and are readily distinguished by their tortuous or spiral form. Having en tered the base of the organ, they spread out into those numerous ramifications which pene trate every part of the ovarian stroma, and give to this structure its peculiar fibrous as pec t. From their extreme branches the blood is returned by the veins, which pass to the base of the organ, where they are very numerous (fig. 370. h). They form, near the ovary and between the folds of the broad ligament, a plexus termed the ovarian or pampiniform plexus, (fig. 369. d) the vessels of which com municate also with the uterine plexus. Valves are found in the ovarian veins only in exceptional cases.
The ovary derives its nerves from the renal and inferior aortic plexuses.* The nerves enter the organ along with the blood-vessels.