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but in it can often be traced as a slight median ridge as far as the uvula vesicæ. When followed in the opposite direction the ridge becomes less marked, and can be followed on the urethral wall into the membranous portion of the canal, where it divides into a pair of inconspicuous folds or elevations, which gradually fade out into the urethral wall (Fig. 1026).
The curvature and, to a less degree, the length of the prostatic urethra depends upon the amount of distension of the bladder and of the rectum (compare Figs. 989 and 990).
Pars Membranacea Urethra.-The second, or membranous portion, of the
FIG. 1026. DISSECTION SHOWING THE TRIGONUM VESICE AND THE POSTERIOR WALL OR FLOOR OF THE URETHRA IN ITS PROSTATIC, MEMBRANOUS, AND THE PROXIMAL PART OF ITS CAVERNOUS SUBDIVISIONS. The canal has been opened up by removing its anterior and upper wail.
urethra leads downwards and forwards from the apex of the prostate to the bulbus urethra, and is the shortest and narrowest of the three subdivisions of the canal, its length being somewhat less than half an inch. It begins at the superior fascia of the urogenital diaphragm, a layer of pelvic fascia which lies above the sphincter urethræ membranacea muscle. Here it is continuous with the prostatic portion of the urethra. It ends, having pierced the inferior fascia of the urogenital diaphragm, by becoming continuous with the cavernous portion of the urethra. Placed in front of the anal canal, it lies about one inch behind and below the arcuate ligament of the pubis (O.T. sub-pubic ligament). It is surrounded by fibres of the sphincter urethræ membranacea muscle, and behind it, on each side of the median plane, lies the bulbo-urethral gland. The posterior part of the bulbus
urethræ projects backwards and overlaps the posterior wall of the membranous part of the urethra to a considerable extent (Fig. 1024).
The membranous portion of the urethra is the most firmly fixed and least dilatable part of the passage.
A slight medial elevation, which is continuous above with the crista urethræ, projects into the canal from its posterior wall, and, becoming less marked as it is traced downwards, is often seen to divide into two faint ridges. When the canal is empty other longitudinal folds or ridges are usually to be seen on the mucous membrane, but these become obliterated when the passage is distended. The lumen of the empty tube, in transverse section, presents a stellate outline.
It is important to note that the terminal portion of the pars membranacea urethræ, where it is overlapped posteriorly by the urethral bulb, lies in front of the urogenital diaphragm. It is considerably wider than the upper part of this subdivision of the canal, and is very thin-walled. This is the part of the canal which is most liable to rupture (Figs. 1024 and 1026).
Pars Cavernosa Urethra.-The third, or cavernous portion, of the urethra is much the longest of the three subdivisions. It begins at a point about half an inch in front of the posterior end of the bulbus urethræ, and ends at the external urethral orifice on the glans penis. Its proximal, or perineal, portion has a fixed position and direction, while its distal part varies with the position of the penis. The canal is about six inches in length, and is related throughout its whole extent to the erectile tissue of the corpus cavernosum urethræ and of the glans penis. Directed at first forwards through the bulbus urethra, the canal turns downwards and forwards at the point where it comes to lie in front of the lower part of the symphysis pubis (Fig. 1025). This bend in the direction of the canal, roughly speaking, corresponds to the place of attachment of the suspensory ligament to the dorsum of the penis. When the penis is drawn upwards towards the front of the abdomen, the direction of the terminal half of the canal is, of course, changed, and at the same time the whole length of this subdivision of the urethra becomes more uniformly curved.
The urethra passing obliquely downwards and forwards enters the bulb at a point nearly half an inch from its posterior extremity. Immediately after the canal has pierced the fascia inferior of the urogenital diaphragm its posterior aspect becomes surrounded by the erectile tissue of the bulb, but the anterior wall remains uncovered for a distance of about a quarter of an inch (Fig. 1025). The wall of the urethra is here very thin, and the passage is more readily dilatable than in other parts. In this region the urethral wall may readily be torn through, if undue force is used, or if the handle is depressed too soon when attempting to pass an instrument into the narrower more fixed part of the canal. The urethra lies at first in the upper part of the erectile tissue, but as it passes forwards it sinks deeper, and comes to occupy the middle part of the corpus cavernosum urethra (Fig. 1025). In the glans, on the other hand, the erectile tissue lies on the dorsal and lateral aspects of the urethra. Like the other parts of the urethral passage, the pars cavernosa is closed except during the passage of fluid, the closure being effected by the apposition of its dorsal and ventral walls except in the portion of the canal which lies in the glans penis, where the side walls of the canal come into contact. Thus the lumen of the first part of the canal, when empty, is represented in cross section by a transverse slit, and that of the terminal part by a vertical slit (Fig. 1027). The cavernous part of the urethra does not present a uniform calibre throughout, but is narrower in its intermediate part, where it traverses the corpus cavernosum urethra, than it is in those portions of its course which are surrounded by the bulb and the glans. The terminal dilated part of the passage is termed the fossa navicularis urethræ, and opens on the surface by the vertically placed slit-like orificium urethræ externum, or external urethral orifice, which is the narrowest and least dilatable part of the whole urethral canal.
The ducts of the bulbo-urethral glands open by very minute apertures in the inferior wall of the proximal part of the cavernous portion of the urethra. Before
opening into the canal, they lie for some distance immediately beneath its mucous membrane. A number of little pit-like recesses, called the lacunæ urethrales, also open into the cavernous part of the urethra, and are so disposed that their openings lead for the most part obliquely into the canal in the direction of its external orifice.
In some cases a somewhat valve-like fold of the mucous membrane, the valvula fossæ navicularis, is found in the upper wall of the urethra in the region of the fossa navicularis. The free edge of this fold is directed towards the external urethral orifice, and may engage the point of a fine instrument introduced into the urethra.
Structure. The mucous membrane of the urethra contains numerous elastic fibres and varies in thickness in different parts of the canal. In many positions it shows distinct longitudinal folds and also minute depressions or pits-the lacunæ urethrales, already mentioned. The lining epithelium is composed of many layers of cells, and is continuous through the internal urethral orifice with the epithelium of the bladder, which at first it closely resembles. In the region of the fossa navicularis the lining cells, which throughout the cavernous portion of the canal are of a columnar type, become flat and scaly.
Numerous minute glands-glandulæ urethrales-open into the urethra. These are most plentiful in the upper, or anterior, wall, but they also occur in smaller numbers in the floor and side walls. They are most numerous in the anterior half of the cavernous portion of the canal, and in the membranous subdivision of the urethra.
The larger glands are deeply placed beneath the mucous coat, and communicate with the urethra by long slender obliquely placed branched ducts. The smaller glands lie in the mucous coat and form flask-like depressions with very short ducts. The ducts of some of the glands open into the lacunæ, but many of the latter have no connexion with the urethral glands.
Frequently two or more elongated ducts belonging to some of the larger glands open into the urethra quite close to its termination. These are sometimes spoken of as paraurethral ducts, and may be traced backwards for some distance beneath the mucous membrane forming the roof of the urethra. Morphologically they do not correspond to the ducts which in the female have received the same name.
The muscular wall in the upper part of the urethra consists of smooth muscle fibres directed for the most part longitudinally, but some circularly arranged fibres are also present. It is probable that throughout the greater part of the cavernous urethra a muscular coat is not represented.
Round the beginning of the urethra there is an obliquely placed band of circularly arranged smooth muscle fibres, which is continued downwards and forwards from below the anterior part of the trigone of the bladder. The lower and anterior fibres of this band lie in the anterior wall of the upper part of the prostatic urethra. The band is sometimes spoken of as the sphincter vesica internus. At a lower level, in front of the prostatic urethra, is a band of striped muscular fibres which is continuous inferiorly with the inner circularly disposed part of the sphincter urethræ membranaceæ.
Like the latter it is probably to be regarded as a part of a primitive voluntary urogenital sphincter muscle, such as is represented also in the female subject.
THE FEMALE REPRODUCTIVE ORGANS.
The reproductive glands in the female are a pair of ovaries placed one on each side of the cavity of the pelvis. In connexion with each ovary is an elongated passage or tube-the uterine (O.T. Fallopian) tube-which leads to the uterus and opens into its cavity. There is no direct continuity between the ovary and the uterine tube, such as exists between the other glands of the body and their ducts, but the ova, when shed from the ovary, pass into the open end of the tube, and are thus conducted to the uterine cavity. The uterus is a hollow muscular organ which
FIG. 1028.-MEDIAN SECTION THROUGH THE FEMALE PELVIS.
Drawn for the most part from a model made from a dissection by Professor Edward H. Taylor.
occupies a nearly median position in the pelvis; it is joined by the uterine tubes above, and it communicates with the upper part of the vagina below. The ovum. having passed through the tube, reaches the cavity of the uterus, and in it, if fertilisation has taken place, the ovum undergoes its development into the embryo and foetus. The vagina is the passage which leads from the uterus to the exterior, and has its external opening behind that of the urethra, within the rima pudendi or uro-genital space. In connexion with the uro-genital space are a number of structures which are included under the term external genital organs, and which represent in the female the various parts of the penis and scrotum in the male. These are the labia majora and the mons Veneris, the labia minora, the clitoris, and the bulbus vestibuli. The larger vestibular glands, placed one on each side of the lower part of the vagina, are accessory organs of the female reproductive system, and are represented by the bulbo-urethral glands in the male.
The ovary is a solid body, flattened from side to side, and about the size and shape of a large almond. Its length is usually between one and one and a half inches, and the thickness from side to side between a quarter and half an inch. In the adult the ovary is placed against the side wall of the pelvic cavity, and is connected by peritoneal folds with the broad ligament of the uterus and with the side wall of the pelvis. The position occupied by the ovary within the pelvic cavity is fairly constant, although these ligaments do not hold the organ firmly fixed in any definite place.
In the ovary we recognise two extremities-a superior extremity, larger and more rounded, and an inferior extremity, somewhat pointed. The term extremitas
FIG. 1029.-SIDE WALL OF THE FEMALE PELVIS, showing the position of the ovary and its relation to the uterine tube. The pelvis has been cut in section parallel to, but at some distance from, the median plane.
tubaria is applied to the superior end of the ovary, as it is most intimately connected with the uterine tube; the term extremitas uterina is used with reference to the inferior extremity, since this part of the ovary is connected with the uterus by a fibrous cord, termed the ligament of the ovary. The flattened surfaces of the Ovary are called facies medialis and facies lateralis, and the borders separating them-margo mesovaricus or mesovarian border, and margo liber or free border. The free border is convex; while the mesovarian, which is straighter and narrower, is connected by a very short peritoneal fold, the mesovarium, with the posterior layer of the broad ligament of the uterus. The vessels and nerves enter the ovary at this mesovarian border, which is therefore often termed the hilum of the ovary.
Position and Relations of the Ovary. When the ovary occupies its most usual, or typical, position the long axis of the gland is vertical. Its lateral surface lies against the wall of the pelvis, and its medial surface looks medially towards the pelvic cavity. The peritoneum of the pelvic wall, where the ovary lies