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 •ANATOMY

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passing along it. It begins at the lowest part of the bladder and for its first inch and quarter passes through the prostate gland and is directed vertically downwards. The hinder wall of this portion is raised into a ridge, the colliculus seminalis, on each side of which the seminal ducts open. The second part is membranous, about 3 inch in length, and directed forwards below the pubes, where it is fixed by passing through the triangular interpubic ligament. The third part is that which lies in the penis, and it is surrounded below and laterally by an erectile enveloping body, the corpus spongiosum urethra. This body begins behind in a thickening, the. bulb of the urethra, and ends in the glans penis,. which is perforated by the urethra. Above the urethra in this, stage he the two corpora cavernosa penis. The urethral orifice is usually the narrowest part of the canal. The female urethra is only H inch in length, and is comparable only with that part of the male urethra which extends. from the bladder to the openings of the seminal ducts (Fig. 12). VII. Reproductive Organs.—In the human male these are the testes and their ducts, the latter being the modified mesonephric or Wolffian tubules and ducts of the foetus. In the female they consist of the ovaries and the tubular system appended to them, which are formed from the modified Mullerian ducts. In each sex the tubular system which is not functional is represented in rudiment. Both ovary and testis are specializations of the area of germinal to ]iold more epithelium of the foetal coelom.. In the ovary these abdomen is opened it can be dilated to more than double germinal cells become grouped in numerous Female. that size. When distended it rises and is applied closely clusters, in the centre of each of which is a cavity, the Graafian vesicle, containing a central ceU larger than the others, which is a primitive ovum. Each of these is about jlfih inch in diameter, and it has been computed that there are about 30,000 m each ovary of a female child at birth. These Graafian vesicles are embedded in a mass of connective tissue which is called the stroma of the ovary, the whole ovary being a sma 1 oval body about U inch long by about ^ inch m thickness. The ovaries are placed one on each side in the pelvic cavity, each within a fold of peritoneum, called the broad ligament. Close to each ovary lies the open and fringed end of a duct the Fallopian tube, which is contained m the upper edge of the broad ligament and directed inwards to. open into the uterus. This is a pyriform organ lying m the middle of the pelvic cavity, having the bladder on its ventral aspect, the rectum on its dorsal, and the two broad ligaments one on each side. The uterus, when not containing a foetus, is about 3 inches in length, nearly L inches in breadth, and 1 inch in thickness. It has a very thick wall mostly made up of unstriped muscle, and a very small cavity which appears somewhat triangular m vertical section. Its lateral basal angles are at the openings whereby the Fallopian tubes communicate with it, and its Fig. 12.—Vertical section through pelvis, shovvinguriMry gadder and rectum apical inferior angle is at the neck or cervix uteri. ihis in situ. 1, peritoneum, 2, ‘I ^hikled • 6 opening of ureter; cervix projects into the upper part of the vagina, which, bladder ; 5, mucous membrane folded ^ ’ns’i0smn ; 14, testis in S, prostate ; 10, vena dorsalis penis ,12, corpus sp0 P g ers of the is a membranous passage that opens on the surface %ac • 15 bulbooavernosus muscle, lt>, duio, j-i, sphinct m The uterus and Fallopian tubes are modifications, ot ’anus *22, anal opening ; 30, coccyx; *, vesicula semmalis. the Mullerian ducts and of the part of the cloaca into against the back of the ventral abdominal wall. The which these ducts open. The vagina and the folds which bladder has a strong muscular investment of unstriped surround its external opening are the modifications of the muscle in several layers, which are innervated by branches urogenital sinus and its marginal folds to be referred to from the sacral nerves. It has a peculiar epi i ,. of several strata, the superficial cells of which are cubic, The ova are during mature life periodically shed, by when the sac is collapsed, but become flattened and scale- rupture of the Graafian follicles when these become ripe. like when it is distended. The bladder is developed from These are received into the open mouths of the T allopia.n the portion of the sac of the embryonic allantois, which is tubes, by which canals they are conducted into the uterus in contact with the cloaca. The two ureters open by where if fertilized they develop, but if not fertl^d ^ small oblique apertures into its base, close y e 1 are extruded. Before fertilization each ovum undergoes a opening of the urethra. The urethra ov excretory channe process of cell division by which it extrudes a poi n in from the bladder is a narrow tube, 83 inches l° g. its nuclear substance and particularly a portion of its male, whose walls are in apposition except when fluid

between the pyramids, ends in minute end-arteries m the cortex. Each of these pierces into one of the flasks just described, and there becomes branched, the branches being collected into a little ball or glomerulus which nearly fills the flask. From this an efferent vessel escapes, which, joining with its neighbouring vessels of the same kind, makes a close network around the convoluted tubes, ultimately ending in the renal vein. It is supposed that the different constituents of the urine are eliminated m different parts of these tubes—some, especially the watery parts, in the flask, and some, especially the more solid constituents^ in the convoluted tubular apparatus. A peculiar form of glandular epithelium lines the two convoluted areas of the tubes, and the limb of the loop nearer the straight or collecting tubes. The ureter or duct of the kidney begins at the hilum and descends on the back wall of the abdominal cavity to open into the bladder. It is usually about 12 inches m length and as thick as a goose quill. At its termination it passes obliquely through the coats of the bladder so that when the bladder is distended the lumen of its end is closed. The urinary bladder is a membranous bag lying in the'pelvic cavity directly behind and above the dorsal surface of the pubes. In the foetus and infant, Bladder however, the bladder lies in the abdomen, not in aad it is 10 seldom distended so urethra. the ^ pelvis. During thanlifeabout oz., but when the