Part 159

The =prostate= is relatively large; it is yellowish in color, dense in structure, and lies at the anterior border of the pubis. It is globular, and surrounds the neck of the bladder and the urethra at their junction. A faint median furrow indicates a division into two lateral lobes. The capsule and stroma contain a large amount of unstriped muscle. The ducts are numerous. Lobules of prostatic tissue (pars disseminata) are also found on the urethra further back. The gland is subject to much variation in size, and is often enlarged, especially in old subjects.

The =uterus masculinus= is a very small saccule (Utriculus prostaticus), often difficult to find.

The =bulbo-urethral= (Cowper’s) =glands= are absent.

The =penis= presents several special features. In its posterior part there are two distinct corpora cavernosa, separated by a median septum penis. In its anterior part there is a bone, the =os penis=, which in large dogs reaches a length of four inches (ca. 10 cm.) or more. It is regarded as a continuation forward of the corpus cavernosum. Ventrally it is grooved for the urethra; dorsally it is convex, and anteriorly it becomes smaller and has a curved fibrous prolongation. The =glans penis= is very long, extending over the entire length of the os penis; posteriorly it forms a rounded enlargement, the =bulbus glandis=; anteriorly it is cylindrical, smaller, and pointed at the extremity. Just in front of the bulbus glandis there is a thick circular layer of glands, forming the =annulus glandularis= (Schmaltz). The two dorsal veins arise from the bulbus glandis, pass backward on the dorsum penis, and unite at the ischial arch. A small muscle (M. compressor venæ dorsalis penis) arises from the tuber ischii on either side; the two converge on the dorsum penis near the bulbus glandis. They compress the dorsal veins, and may also tend to elevate the penis and thus assist in copulation. The other muscles offer no features worthy of special description.

The =prepuce= forms a complete sheath around the anterior part of the penis. The outer layer is ordinary integument. The inner layer has the character of a glandular mucous membrane; it is thin and reddish in color. The penile layer is glandless. In the fundus of the præputial cavity there are numerous lymph follicles. The protractor muscles arise in the xiphoid region and decussate posteriorly around the extremity of the penis.

FIG. 405.—EXTERNAL GENITAL ORGANS OF MALE DOG, VENTRO-LATERAL VIEW OF PREPARATION.

1, Scrotum; 1′, tunica vaginalis; 2, epididymis; 3, vascular part of spermatic cord; 4, vas deferens; 5, prepuce; 6, glans penis; 6′, corpus cavernosum penis; 7, bulbus glandis; 7′, contour of bulbus in erection; 8, ischio-cavernosus muscle; a, acetabulum; b, obturator foramen. (After Ellenberger, in Leisering’s Atlas.) ]

FIG. 406.—INTERNAL GENITAL ORGANS OF MALE DOG.

1, Urinary bladder; 2, ureter; 3, vas deferens; 4, prostate; 5, urethral muscle; 6, bulb of urethra; a, abdominal wall; b, ilium; c, ischium. (After Ellenberger, in Leisering’s Atlas.) ]

The pelvic part of the =urethra= is relatively long. Its first part is inclosed in the prostate. At the ischial arch the urethra has a well-developed bilobed =bulb=, formed by an enlargement here of the corpus spongiosum. It is covered by the strong but short bulbo-cavernosus muscle. The other erectile bodies have been described.

The =urethral= (Wilson’s) =muscle= is very strong; it encircles the urethra and has a median raphé dorsally.

THE FEMALE GENITAL ORGANS

The =female genital organs= (Organa genitalia feminina) are: (1) The two =ovaries=, the essential reproductive glands, in which the ova are produced; (2) the =uterine= or =Fallopian tubes=, which convey the ova to the uterus; (3) the =uterus=, in which the ovum develops; (4) the =vagina=, a dilatable passage through which the fœtus is expelled from the uterus; (5) the =vulva=, the terminal segment of the genital tract, which serves also for the expulsion of the urine; (6) the =mammary glands=, which are glands of the skin, but are so closely associated functionally with the generative organs proper as to be described with them.

GENITAL ORGANS OF THE MARE

THE OVARIES

FIG. 407.—LATERAL VIEW OF GENITAL ORGANS AND ADJACENT STRUCTURES OF MARE.

The removal of the other abdominal viscera has allowed the ovaries and uterus to sink down, whereas they are normally in contact with the roof of the cavity in the non-pregnant subject. 1, Left ovary; 2, Fallopian tube; 3, left cornu uteri; 4, right cornu uteri; 5, corpus uteri; 5′, portio vaginalis uteri, and 5″, os uteri, seen through window cut in vagina; 6, broad ligament of uterus; 6″, round ligament; 7, vagina; 8, labia vulvæ; 9, rima vulvæ; 9′ superior commissure, and 9′, inferior commissure of vulva; 10, constrictor vulvæ; 11, position of vestibular bulb; 12, ventral wall of abdomen; 13, left kidney; 14, left ureter; 15, urinary bladder; 16, urethra; 17, rectum; 18, anus; 19, 19′, unpaired and paired parts of sphincter ani externus; 20, retractor ani cut at disappearance under sphincter; 21, suspensory ligament of anus; 22, longitudinal muscular layer of rectum; 22′, recto-coccygeus; 23, constrictor vaginæ; a, utero-ovarian artery, with ovarian (a′) and uterine (a″) branches; b, uterine artery; c, umbilical artery; d, ischium; e, pubis; f, ilium. (After Ellenberger, in Leisering’s Atlas.) ]

The =ovaries= (Ovaria) of the mare are bean-shaped, and are much smaller than the testicles. Their size varies much in different subjects, and they are normally larger in young than in old animals; one ovary is often larger than the other. They are about three inches (ca. 7 to 8 cm.) long and an inch to an inch and a half (ca. 3 to 4 cm.) thick. The weight is about two and a half to three ounces (ca. 70 to 80 grams).

Each presents for description two surfaces, two borders, and two extremities or poles. The =surfaces= are termed internal and external (Facies medialis, lateralis); they are both smooth and rounded. The =attached= or =mesovarial border= (Margo mesovaricus) is convex. It is inclosed in a part of the broad ligament termed the mesovarium; the vessels and nerves reach the gland at this border. The =free border= (Margo liber) is marked by a notch which leads into a depression, the =ovulation fossa=. The =tubal= or =anterior extremity= (Extremitas tubaria) is rounded, and is related to the fimbriated end of the uterine or Fallopian tube. The =uterine= or =posterior extremity= (Extremitas uterina) is also round, and is connected with the horn of the uterus by the ovarian ligament.

The ovaries are situated in the sublumbar region of the abdominal cavity, about a handbreadth behind the corresponding kidney. They are in contact with the lumbar wall of the abdomen, and are commonly about two or three inches (ca. 5 to 7.5 cm.) from the median plane. The distance from the ovaries to the vulvar orifice is about twenty inches (ca. 50 cm.) in a mare of medium size. The attached (mesovarial) border is commonly directed toward the median plane, the free border laterally and somewhat ventrally.

The position of the ovaries is not constant, but is subject to less variation than might be expected from their mode of attachment. The normal variations in the non-pregnant state are chiefly in a transverse direction, and do not usually exceed two or three inches (ca. 5 to 7 cm.). It is not at all rare to find the ovary deflected medially, so that the external surface faces ventrally. In the longitudinal direction little variation appears to occur. The right ovary is usually about four or five inches (ca. 10 to 12 cm.), and the left one about three or four inches (ca. 8 to 10 cm.), behind the corresponding kidney. Thus they lie about in a transverse plane tangent to the external angles of the ilia, i. e., through the fifth lumbar vertebra. They may be about two inches (ca. 5 cm.) from the extremity of the corresponding cornu of the uterus or in contact with it. The right ovary commonly lies a little (ca. 2.5 cm.) further forward than the left one. Except during pregnancy, they are normally in contact with the lumbar abdominal wall, and do not hang down among the adjacent viscera.

FIG. 408.—RIGHT OVARY OF MARE, WITH ADJACENT STRUCTURES.

The extremity of the cornu uteri is opened. 1, Ovary; 2, Fallopian tube, with its ostium abdominale (2′), fimbriæ (2″), and ostium uterinum (2‴); 3, cornu uteri, with its mucous lining (3′); 4, ovarian ligament; 4′, mesosalpinx. (After Ellenberger, in Leisering’s Atlas, reduced.) ]

The ovary is attached to the sublumbar region by the anterior part of the broad ligament; this part of the ligament, the =mesovarium=, is about three or four inches (ca. 8 to 10 cm.) wide, measured from the ovary directly to the parietal attachment. The uterine or posterior extremity of the ovary, is connected with the extremity of the cornu of the uterus by the =ovarian ligament= (Ligamentum ovarii proprium); this is a band of unstriped muscle inclosed between the layers of the broad ligament.

=Structure.=—The greater part of the surface of the ovary has a covering of peritoneum. The peritoneal investment is absent at the attached border where the vessels and nerves enter; this area is termed the =hilus=. The ovulation fossa is covered by a layer of columnar cells, a remnant of the primitive =germinal epithelium=. The =stroma= of the ovary (Stroma ovarii) is a network of connective tissue and unstriped muscular fibers. In the deeper or medullary portion of the stroma (Zona vasculosa) the meshes are largely occupied by the numerous blood-vessels. In the peripheral or cortical portion (Zona parenchymatosa) are numerous =ova= (Ovula) in various stages of development. The immature ova are surrounded by follicle cells; those more advanced in development are inclosed also by a condensation of the stroma termed the =theca folliculi=; within the theca is a quantity of fluid, the =liquor folliculi=. These constitute the =Graafian follicles= (Folliculi oöphori), which enlarge as they mature, becoming visible to the naked eye as vesicles with a diameter of a centimeter or more. When fully developed, the follicles are superficially situated, and often project slightly from the surface of the ovary. At intervals follicles rupture and their contents escape. This process, which sets free the ovum, is termed =ovulation=; it takes place in the mare only at the ovulation fossa, and occurs during the periods of œstrum.

FIG. 409.—SCHEMATIC REPRESENTATION OF CHANGES IN OVARY OF MARE FROM FŒTAL TO ADULT STATE. (After Born.)

The changes affect chiefly the free border (upper in figure) and the extent and form of the area covered by germinal epithelium (4). 1, Peritoneum (broad ligament); 2, ligament of ovary; 3, fimbria of Fallopian tube; 4, germinal epithelium; 5, vessels, which reach the ovary at the attached border (6). The latter represents the hilus, while the deep depression at the free border is the ovulation fossa. (Ellenberger, in Leisering’s Atlas.) ]

After rupture of a follicle its cavity is partly occupied by a blood-clot, constituting what may be termed a =corpus rubrum=. By proliferation and enlargement and fatty changes, the follicle cells are transformed into lutein cells, forming a yellow mass known as a =corpus luteum=. If impregnation takes place, the accompanying increase in vascularity of the organs may cause the corpus luteum to reach a large size; if impregnation does not occur, it is much smaller, and is sooner replaced by scar tissue, the =corpus albicans=.