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10 External abdominal oblique 10' Pelvic tendon

10'' Abdominal tendon

11 Transversus abdominis

12 Transverse fascia

12' Internal spermatic fascia

13Peritoneum 13' Vaginal ring

13'' Vaginal process

14External pudendal vessels

15Rectus abdominis

16Supf. inguinal ring

17Testicular vessels

18Linea alba

19 Fascia lata

20 Scrotal septum

(vide p. 73, 77)

3.Prepubic Tendon, Inguinal Canal of the Mare, Nerves of the Lumbar Plexus, Hypaxial Lumbar Muscles, and Udder

a)PREPUBIC TENDON

1The prepubic tendon (2) is a strong, transversely oriented, fibrous mass set against the pecten of the pubis and extending from one iliopubic eminence to the other. The prepubic tendon is formed principally by the right and left pectineus (and adductor longus) muscles (5) whose tendons of origin, after arising from the pecten on both sides of the median as far laterally as the iliopubic eminences, decussate ventromedial to the pelvic symphysis. (The tendinous cranial parts of the gracilis and external obturator muscles also take part in its formation.)

The inguinal ligament (1) together with the pelvic tendon of the external abdominal oblique join the lateral parts of the prepubic tendon. The accessory ligament (4), the insertion tendon of the rectus abdominis, perforates, but also attaches itself to, the prepubic tendon and eventually passes via the acetabular notch to the fovea on the femoral head, accompanied the last few cm by the ligament of the femoral head (3).

2The linea alba (14) is formed by the convergence of the aponeuroses of the flat abdominal muscles in the ventral midline. It is several cm wide near the umbilicus, but narrows to a few mm as it joins the prepubic tendon between the bellies of the rectus muscles.

b)STRUCTURES ASSOCIATED WITH THE INGUINAL CANAL OF THE MARE

The evaginations of the peritoneum (19, not shown on this side but at 12), the transverse fascia (12), and the abdominal tunic (13) are much less prominent than in the male, not always present, and difficult to demonstrate. The round ligament of the uterus (11) contains small amounts of smooth and striated muscle and presents a small, pendulous appendage near its origin from the uterine horn.

It and a rudimentary cremaster muscle can be traced through the inguinal canal to where they end at the base of the udder. (In the specimen from which the lower Fig. on the facing page was drawn, the cremaster [see p. 75.4] was relatively well developed.)

c) THE NERVES OF THE LUMBAR PLEXUS (VENTRAL BRANCHES OF L2

TO L6)

Nerve L1 continues solely the ventral branch of the first lumbar nerve and thus cannot be regarded as belonging to the lumbar plexus, though it is often described under that heading. It takes a subperitoneal course to the vicinity of the deep inguinal ring and takes part in the innervation of the caudal parts of the internal abdominal oblique and the transversus abdominis muscles. Its sometimes double lateral cutaneous branch perforates (and also supplies) the abdominal muscles to innervate the skin and the fold of the flank.

Nerve L2 (18; with contribution from L3) also supplies the skin and the fold of the flank with its lateral cutaneous branch. It crosses the ventral surface of the deep circumflex iliac vessels (9), shortly before the latter penetrate the flank, to pass with one or two branches through the lateral part of the supf. inguinal ring.

The lateral cutaneous femoral nerve (10; from L3 and 4) obliquely crosses the dorsal surface of the deep circumflex iliac vessels and then accompanies their caudal branch through the body wall to the flank fold.

The genitofemoral nerve (20; from L2 to 4) crosses the deep circumflex iliac vessels more medially with one or two branches and passes through the medial part of the supf. inguinal ring.

The femoral and, its branch, the saphenous nerves (see p. 19.12; 19.25; from L4 to 6) were described on p 18.

Also the obturator nerve (see p. 19.5; from L4 to 6) was already described on p. 18.

Clinical and Functional Anatomy p. 173

d) HYPAXIAL LUMBAR MUSCLES

For psoas major (7), psoas minor (8), and quadratus lumborum

(not shown) consult the Tables on the musculature on p. 99.

e) UDDER

The udder of the mare lies ventral to the area where the ventral 3 abdominal wall joins the bony pelvis. Its shape and size are related

to the functional state of the ovaries. It is a relatively small gland, hardly noticeable in the virgin mare but rounded and semispherical during the latter part of pregnancy and subsequent lactation. One hair (or more) protruding from the teat orifice, as well as other less obvious features remind us that the mammary gland is an enormously enlarged apocrine sweat gland. The hair disappears at the beginning of lactation or is worn off by the foal during suckling. Secretions of both sebaceous and sweat glands in the tip of the teat (or perhaps precocious colostrum) fill the two teat orifices and cover the tip of the teat with a waxy material whose presence indicates that foaling is imminent.

The udder (see Fig. on this page) comprises right and left mammary glands (15) each surmounted by a teat (17). Each gland accommodates two (sometimes three) duct systems which channel the milk through increasingly larger lactiferous ducts (B) into a lactiferous sinus (A) in the base of the teat and in the teat itself (teat sinus). Two papillary ducts (C) ending at the teat orifices (D) convey the milk to the outside. Though the two duct systems in each half of the udder are separate, the glandular tissue belonging to each can only be demonstrated by injections of different color suspensions into the two orifices. (For blood and nerve supply of the udder see p. 80.)

The udder is supported by a suspensory apparatus (21) that comprises medial and lateral laminae. The paired medial lamina (21') is elastic and arises from the abdominal tunic near the linea alba and separates the two halves of the udder along the prominent intermammary groove (16). The lateral laminae (21'') are less elastic though they arise also from abdominal tunic but in the vicinity of the supf. inguinal rings from where they pass lateral to the glandular tissue and separate it from a layer of adjacent fat.

Udder, sagittal section through a teat

15

1 Inguinal ligament

Pelvic tendon of ext. abdominal oblique

1' Rectus abdominis, fenestrated

2Prepubic tendon

3Ligament of head of femur

4Accessory ligament

5Pectineus (and adductor longus) Symphysial tendon fossa

(ventral view)

14

3

3

5 4

4

1

2

(ventral view)

a

q

7Adrenal glands

8Left kidney

9Ureter

10Deep circumflex iliac vessels 10' Cranial branch

10'' Caudal branch

11Lateral and round ligaments of bladder

12Median ligament of bladder

(See p. 63 and 69)

Right Kidney

sectioned through hilus and poles

13 Renal pelvis

14 Terminal recesses

15 Renal lobes

20'' 14

20'

16 Renal cortex

17 Renal hilus

18 Renal sinus

19 Interlobar vessels

20 Medulla

20' External part 20'' Internal part 20''' Renal crest

Left Kidney

cast of renal vessels and renal pelvis

b

9

13

s

1a) The ABDOMINAL AORTA (2) begins its break-up already at the level of the 5th lumbar vertebra. It gives rise to the paired external and internal iliac arteries, and to the unpaired median sacral artery which is occasiomnally absent.

The external iliac artery (10), seldom the internal iliac, in the mare releases the uterine artery (11), the principal artery of the uterus, and in the stallion it releases the cremasteric artery (11) which accompanies the testicular artery (from the aorta) through the vaginal ring. Before entering the vascular lacuna to gain the thigh, the external iliac gives rise to the deep femoral artery (12) which in turn gives off the pudendoepigastric trunk (13). This immediately gives off the external pudendal artery (15) which passes through the inguinal canal. The external pudendal, among other branches, supplies vessels for the udder and the cranial artery of the penis (19) which anastomoses on the dorsal surface of the penis with the middle artery of the penis (46; from the obturator) and the dorsal artery of the penis (38; from the internal pudendal).

The internal iliac artery (22), as does the abdominal aorta and sometimes also the caudal gluteal, sends lumbar arteries (3) to the vertebral column and associated structures, and immediately (opposite the 6th lumbar vertebra) divides into the caudal gluteal (47) and internal pudendal arteries (23). Of these the former is destined predominantly for the pelvic wall, while the latter goes to the pelvic viscera.

The internal pudendal artery (23), close to its origin, gives off the umbilical artery (24) which, in the stallion, releases the small artery of the deferent duct (25), and in both sexes the cranial vesical artery (26) and ends as the round ligament of the bladder (27) in the free border of the lateral ligament of the bladder. The internal pudendal then courses along the medial surface of the sacrosciatic ligament in the vicinity of the pudendal nerve and with its next branch, the vaginal artery (prostatic in the male) (28), supplies most of the pelvic viscera: branch to deferent duct or uterine branch (29), caudal vesical artery (30), ureteric branch (31), urethral branch (32), middle rectal artery (33), ventral perineal artery (40), and the caudal rectal artery (41). The internal pudendal itself is continued by the artery of the penis (36); the clitoris receives its supply from the middle clitoral artery, a branch of the obturator artery.

The caudal gluteal artery (47) and its branches, especially the cranial gluteal artery (49) that exits by the greater sciatic foramen, supply the dorsolateral wall of the pelvis and the croup. The obturator artery (44), arising either from the caudal or cranial gluteal, is the exception: it passes caudoventrally on the medial aspect of the shaft of the ilium and leaves the pelvic cavity together with its satellite vein and nerve by the obturator foramen. Below the floor of the pelvis it detaches the middle artery of the penis (clitoris) (46).

b) The VEINS of the pelvic cavity by and large are satellite to the arteries; deviations are shown in the Figures on the opposite page.

The external pudendal vein (15) that accompanies its satellite artery through the inguinal canal is very thin. Its blood-return function is assumed by the accessory external pudendal vein (16) which collects most of the veins from penis or udder and delivers the blood to the ipsilateral deep femoral vein (branch of external iliac) at the cranial end of the pelvic symphysis. Right and left accessory external pudendal veins anastomose here (in the symphysial fossa; see p.

73.3) across the median plane; it is the transected anastomosis that attracts attention after the hind quarters of the cadaver are split (see p. 83). The large obturator vein (44) assists the accessory external pudendal vein in draining penis and udder.

The blood supply of penis and udder follows in greater detail.

c) The BLOOD SUPPLY OF THE PENIS derives from three sets of vessels: internal pudendal artery and vein, obturator artery and vein, and external pudendal artery and the accessory external pudendal vein. The internal pudendal artery (23) becomes the artery of the

penis (36) which gives rise to the artery of the bulb (37) for the bulb and corpus spongiosum, and to the dorsal artery of the penis (38) which anastomoses with the middle (46) and cranial (19) arteries of the penis on the dorsal surface of the organ. The deep artery of the penis (39) for the corpus cavernosum carries blood from the obturator artery. The veins form an extensive plexus dorsal and lateral to the penis whose blood enters the accessory external pudendal vein (16) but also the obturator (44) and internal (23) pudendal veins.

d) The BLOOD SUPPLY OF THE UDDER comes fom the external pudendal artery via the caudal supf. epigastric (cranial mammary artery; 20) and from the internal pudendal artery via the dorsal labial branch that anastomoses with the ventral labial branch (caudal mammary artery; 18) of the external pudendal.

The venous drainage is mainly by the accessory external pudendal vein (middle mammary vein; 16) into the deep femoral, but also by the caudal supf. epigastric vein (cranial mammary vein; 20) and by the ventral labial vein of the external pudendal (caudal mammary vein; 18) which anastomoses with the dorsal labial vein of the internal pudendal.

e)The BLOOD SUPPLY OF THE UTERUS comes principally from the uterine artery (11), a branch of the external (rarely internal) iliac.

The uterine artery anastomoses cranially with the uterine branch of the ovarian artery (5) and caudally with the uterine branch of the vaginal artery (29).

f)The SACRAL PLEXUS OF NERVES is the continuation of the lumbar plexus; together they form the lumbosacral plexus (see p. 76).

The cranial gluteal nerve (L6–S2; f) accompanies the like-named artery through the greater sciatic foramen to supply the gluteus medius, accessorius, and profundus, and also the tensor fasciae latae (see p. 19.8).

The sciatic nerve (L5–S2; g) also emerges from the greater sciatic foramen. Lying on the sacrosciatic ligament, it passes the hip joint dorsally and caudally, and as the largest nerve of the plexus enters the pelvic limb.

The caudal gluteal nerve (L6–S2; h) passes also through the greater sciatic foramen and accompanies like-named blood vessels into the gluteus supf. and into the vertebral heads of biceps and semitendinosus.

The caudal cutaneous femoral nerve (S1–S2; i) at first follows the dorsal border of the sciatic nerve but as the latter turns ventrally into the limb, it passes over the ischial tuber to end subcutaneously on the caudal surface of the thigh.

The pudendal nerve (S2–S4; j) at first lies on the medial surface of the sacrosciatic ligament, and then within the ligament, in which position it reaches the lesser sciatic foramen. Here it communicates with the caudal cutaneous femoral nerve. Before accompanying the internal pudendal vessels to the penis (clitoris), it gives rise to the deep perineal nerve (l) for the striated muscles of the perineum and the supf. perineal nerve (m) which is sensory to the vulva and perineal body.

The caudal rectal nerve (S4, S5; k) passes caudoventrally and supplies sensation to rectum, anal canal, and perineum; it also contributes to the motor innervation of the perineal musculature.

g) For the AUTONOMIC NERVOUS SYSTEM at the entrance to the pelvic cavity we need merely mention that the caudal mesenteric ganglion

(o) lies cranioproximal to the origin of the caudal mesenteric artery

(7), and that the hypogastric nerve (p), which begins here, at first follows the roof of the cavity and then descends to the pelvic plexus

(q) on the viscera. The parasympathetic pelvic nerves (r) arise from the roots of the pudendal and caudal rectal nerves, pass ventrally, and join the pelvic plexus.

1Caudal vena cava

2Abdominal aorta

4Ovarian or testicular vessels

5Uterine branch

6Pampiniform plexus

7Caudal mesenteric artery

8Common iliac vein

9Deep circumflex iliac vessels

10External iliac vessels

11Uterine or cremasteric vessels

12Deep femoral vessels

13Pudendoepigastric arterial trunk

aIlioinguinal nerve (L2)

bGenitofemoral nerve

cLateral cutaneous femoral nerve

dFemoral nerve

eObturator nerve

fCranial gluteal nerve

gSciatic nerve

hCaudal gluteal nerve

iCaudal cutaneous femoral nerve

jPudendal nerve

kCaudal rectal nerves

lDeep perineal nerve

mSupf. perineal nerve

nDorsal nerve of penis (clitoris)

oCaudal mesenteric ganglion

pHypogastric nerve

qPelvic plexus

rPelvic nerves

L3 L4

3

2

1

a

4

L3 L4

3

2

1

a

L5

c

b

7 o

5 9

L5

c

b

o

7

9

4

14

20

52

50

51

k

36

37

46 39

38

6. Female Reproductive Organs

1a) The OVARY (10) is relatively very large (about 8 by 5 cm) lies about 10 cm caudal to the kidneys and, when projected onto the skin, the same distance cranioventral to the coxal tuber, i.e., at the level of the 5th lumbar vertebra. The ovary is suspended by the 15 cm long mesovarium (2) whose cranial border (suspensory ligament of the ovary; 1) extends on the sublumbar area towards the diaphagm. The mesovarium splits off the mesosalpinx (3) from its lateral surface and is continued caudally by the mesometrium (4). The three sheets taken together constitute the broad ligament.

The oval ovary of the filly gradually takes on the shape of a bean. This is brought about by regression of the cell masses in the stroma

(cessation of the hormonal influence), more rapid growth at the poles, and progressive indentation at the free border to form the ovulation fossa. The germinal epithelium is concentrated in the area of the fossa which thus is the only region on the surface of the organ where ovulation can occur. The remainder of the ovary is covered by peritoneum (flat mesothelial cells) which has a slightly different color than the germinal epithelium. The parenchymatous zone containing the follicles lies deep to the germinal epithelium and thus surrounds the depth of the ovulation fossa. (In the filly, before the fossa developed, the parenchymatous zone covered (cap-like) the free border of the ovary.) The vascular zone of the adult ovary is relegated to the poles and attached border. The concept of the parenchymatous zone forming a cortex and the vascular zone forming a medulla, as is the case in other domestic mammals, does not apply in the mare.

The surface of the ovary is relativelty flat, and corpora lutea, even at their largest, do not become conspicuous. Likewise, mature follicles, which can attain a diameter of 6 cm, bulge only slightly fom the surface; they are not as easily recognized on rectal exploration as in the cow where the ovaries are considerably smaller.

b) The UTERINE TUBE (14) meanders—parallel to the body axis— from the ovulation fossa to the horn of the uterus. It is suspended in the mesosalpinx (3) that arises from the lateral surface of the mesovarium and ends with a free border a few mm ventral to the uterine tube. The mesosalpinx forms the lateral, and the proper ligament of the ovary (6) the medial wall of the shallow ovarian bursa (5) which has a wide entrance, open ventrally, for easy access to the ovary.

Ovary

Tertiary (vesicular) follicles

Parenchymatous zone (cortex)

Periodic corpus luteum

Corpus albicans

Atretic corpus luteum Vascular zone

Ovulation fossa

Fimbriae of infundibulum

2 The infundibulum (16), the funnel shaped ovarian end of the uter-

nal orifice of the tube, situated in the center of the infundibulum, faces the ovary and leads into the shorter wide part (ampulla) of the tube. Depending on the phase the cycle, the ampulla may attain a diameter of 6 . The longer remainder (isthmus) of the tube is only half as wide and ends with its uterine orifice (15) on the tip of the uterine horn where it raises a small papilla that contains a sphincter.

3c) UTERUS. Horns (11) and body (12) are of about equal length (25

4cm each). Both are in the abdominal cavity; only the cervix, which is about 6 cm long, lies in the pelvic cavity where it rests on bladder

82

Clitoris, caudal view of glans

Glans

Clitoral sinuses

Transverse fold forming dorsal part of prepuce

23 24

Ventral commissure (of labia)

1Suspensory ligament of ovary Broad ligament:

2Mesovarium

3Mesosalpinx

4Mesometrium

5Ovarian bursa

7. Male Reproductive Organs

1a) The TESTES (19; t) lie in the pubic region between the cranial parts of the thighs. Their long axes almost match that of the trunk, but change to a nearly dorsoventral direction when the testes are drawn up by the cremaster muscles. The testes are anchored to the parietal layer of the vaginal process by the mesorchium (v') and by the ligament of the tail of the epididymis (w). The latter forms the caudal end of the mesorchium and is attached to the dartos that lines the scrotum by a condensation of connective tissue forming the scrotal ligament. The proper ligment of the testis (x) connects the caudal pole of the testis to the tail of the epididymis.

The testis has the shape of a bilaterally compressed, shortened egg.

The arterial pattern visible on the surface is characteristic for the

2species. A major branch of the testicular artery (20) appears close to the tail of the epididymis and meanders along the free border of the testis toward the cranial pole where it breaks up. Tortuous branches given off during its course supply both sides of the organ. The testicular parenchyma, on section, appears yellowish gray; the mediastinum testis and the rete testis it contains are indistinct and concentrated at the cranial pole close to the head of the epididymis.

b) The head (14) of the EPIDIDYMIS does not extend beyond the cra-

3nial pole of the testis, but the tail (16) is larger and projects well

4beyond the caudal extremity of the testis so that it can be palpated without difficulty. Between the head and the tail is the body of the epididymis (15) which forms the testicular bursa (17) with the dorsal part of the lateral surface of the testis.

5c) There is a full complement of ACCESSORY REPRODUCTIVE GLANDS consisting of seminal vesicle, ampulla of the deferent duct, prostate, and bulbourethral gland. These are fully developed in the stallion and retain their juvenile status following castration in the gelding. The seminal vesicle (11) and the ampulla of the deferent duct (10, whose wall is thickened by glands) lie on the dorsal surface of the bladder with the ureter between them. The seminal vesicle is homologous to the vesicular gland of ruminant and pig but because of its central collecting space carries a different name. Its duct joins the deferent duct forming a short ejaculatory duct that opens on the colliculus seminalis where it is flanked by several openings of the ducts of the prostate (see p. 78). The knobby right (12) and left (13) lobes of the prostate are connected by an isthmus dorsal to the urethra. There is no disseminate part. The paired bulbourethral glands (18) lie at the level of the pelvic oulet. Their medial surfaces especially are covered by the bulboglandularis (18, part of m. ischiourethralis). The ducts open in two rows on the dorsal surface of the urethra as the latter proceeds to pass ventrally around the ischial arch.

6d) PENIS and PREPUCE (sheath) present several features characteristic of the horse (see also the Fig. on this page). The prepuce proper, comparable to that of the other domestic mammals, is a sleeve with internal and external surfaces (laminae; 5; 6) of which the latter is the skin. Where the two surfaces become confluent cranially, the

tunica albuginea renders it softer in the erected state than the corpus cavernosum; this is thought to protect the female organs during coitus. The cranial surface of the glans is recessed ventrally to form the fossa glandis (E) from which the free end of the urethra (urethral process) with its external urethral orifice protrudes slightly. The greatest circumference of the glans is the corona glandis (F) which often carries short papillae. The abrupt narrowing of the glans proximal to the corona is known as the neck of the glans (collum glandis). Dorsally, the glans is continued proximally by a dorsal process, about 10 cm long, that lies on the corpus cavernosum without external demarkation and is visible only upon sectioning.

The muscles of the horse's penis are well developed. The ischiocavernosus (8) typically lies in a depression of the semimembranosus.

It arises from the ischial arch close to the ischial tuber and caudal border of the sacrosciatic ligament and surrounds the crus of the penis of the same side. During erection the ischiocavernosi contract rhythmically to pump arterial blood that has entered the corpus cavernosum forward, and at the end of sexual excitement allow the blood to leave the penis again. The bulbospongiosus (7) begins near the bulbourethral glands, covers the bulb of the penis (7) and reaches apically to the free part of the penis. Its transverse fibers connect the edges of the urethral groove to contain urethra and corpus spongiosum. The smooth retractor penis (9) takes origin from the caudal vertebrae and with right and left parts descends on each side of the rectum. The two parts unite and decussate below the rectum where two narrow bands of muscle arise to lie on the caudal, and later ventral, surface of the bulbospongiosus. As the two retractor bands approach the free part of the penis, they work their way through the transverse fibers of the bulbospongiosus so that the latter muscle then lies ventral to the retractor.