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Fascia Transversalis.-The fascial lining of the abdominal cavity (fascia transversalis) consists of a continuous layer of membrane which receives different names in different parts of its extent. It covers the deep surface of the transversus muscle, and is continuous medially with the fascia of the quadratus lumborum and the psoas muscles. It is continuous above with the diaphragmatic fascia, and below the iliac crest and the inguinal ligament with the fascia iliaca. Along with the last-named fascia it forms the femoral sheath, enclosing the femoral vessels and the femoral canal in their passage to the thigh behind the medial part of the inguinal ligament (p. 405). It is pierced by the spermatic funiculus or

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round ligament of the uterus at the abdominal inguinal ring, and its prolongation. into the inguinal canal around the funiculus forms the internal spermatic or infundibuliform fascia. It is lined internally by the peritoneum, from which it is separated by a layer of extraperitoneal tissue.

The subserous coat or extraperitoneal tissue is usually loaded with fat; it envelops the kidneys, ureters, suprarenal glands, abdominal aorta and inferior vena cava and their branches, and forms sheaths for the vessels and ducts (ureter, ductus deferens, etc.). It is continued upwards into the posterior mediastinum of the thorax through the aortic opening in the diaphragm, and below is in continuity with the extraperitoneal tissue in the pelvis. It not only completely invests the kidneys and suprarenal glands, but it also becomes interpolated between the layers of peritoneum upholding and enveloping the intestines. This tissue is absent in relation to the diaphragm, on the under surface of which there is no fat.

THE MUSCLES OF THE ABDOMINAL WALL.

The muscles of the abdominal wall are in three series-lateral, anterior, and posterior. The lateral muscles of the abdominal wall comprise the obliquus externus abdominis, obliquus internus abdominis, and transversus abdominis.

M. Obliquus Externus Abdominis.-The obliquus externus abdominis is a broad thin sheet of muscle, with an origin from the lateral surfaces of the lower eight ribs, by slips which interdigitate with the serratus anterior and latissimus

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dorsi muscles. The muscular fibres radiate downwards and forwards, the lowest fibres passing vertically downwards.

The muscle fibres of the lower and posterior part of the muscle are inserted, directly, into the external lip of the iliac crest in its anterior half or two-thirds (Fig. 369, p. 415). The rest of the muscle fibres are inserted into an extensive triangular aponeurosis which forms part of the anterior abdominal wall. This aponeurosis is broader below than above; it is united with part of the aponeurosis of the obliquus internus in the superior three-fourths of its extent, to form the anterior layer of the sheath of the rectus muscle. It thus gains an attachment, above to the xiphoid process, below to the symphysis pubis, and by its intermediate fibres to the linea alba.

The linea alba is a band of interlacing fibres, about half an inch in width at its widest part. It occupies the median plane of the anterior abdominal wall in its whole extent, is pierced by the umbilicus (annulus umbilicalis), and forms the greater part of the ultimate insertion of all the lateral abdominal muscles.

The superior part of the aponeurosis covers the insertion of the rectus abdominis muscle on the chest wall, and gives origin to fibres of the pectoralis major. Inferiorly, in the groin, the lower part of the aponeurosis gives rise to the inguinal ligament, the ligamentum lacunare, the two crura of the subcutaneous inguinal ring, the external spermatic fascia and the intercrural fibres, and the ligamentum inguinale reflexum of Colles.

Lig. Inguinale [Pouparti].-The inguinal ligamentum (O.T. Poupart's ligament) is an aponeurotic band which extends from the anterior superior iliac spine to the tubercle of the pubis, arching over the iliacus, psoas, and pectineus muscles. It represents the inferior margin of the aponeurosis of the obliquus externus abdominis, and it gives attachment below to the iliac portion of the fascia lata of the thigh. Its lateral part affords partial origin to the obliquus internus and transversus muscles, and receives the attachment of the fascia transversalis and fascia iliaca; the medial part forms the gutter-like floor of the inguinal canal. At its medial end a triangular band of fibres is reflected horizontally backwards to the ilio-pectineal line, forming the lig. lacunare [Gimbernati] (O.T. Gim

bernat's ligament), Fascia transversalis

Peritoneum

OBLIQUES EXTERNUS

'OBLIQUUS INTERNUS
TRANSVERSUS
ABDOMINIS

the lateral edge of which forms the medial boundary of the femoral ring. The femoral vessels, enclosed in the femoral sheath,

tissue

enter the thigh Extraperitoneal posterior to the

inguinal ligament,

surface of the psoas major muscle, and the term superficial femoral arch is given to the part of the ligament which covers the vessels.

Colon

Kidney

on the anterior Posterior aponeurosis

of transversus

LATISSIMUS DORSI
QUADRATUS LUMBORUM,

RECTUS ABDOMINIS

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Middle layer of lumbo-dorsal fascia

Duodenum

Psoas fascia

Second lumbar vertebra

PSOAS MAJOR

Anterior layer of -lumbo-dorsal fascia

MULTIFIDUS

SEMISPINALIS

DORSI

ILIOCOSTALIS

Posterior layer of lumbo-dorsal fascia

LONGISSIMUS DORSI FIG. 423.-TRANSVERSE SECTION THROUGH THE ABDOMEN, OPPOSITE THE SECOND LUMBAR VERTEBRA.

Annulus Inguinalis Subcutaneus. The subcutaneus inguinal ring (O.T. external abdominal ring), the place of exit of an inguinal hernia, is a split in the aponeurosis of the obliquus externus, just above the tubercle of the pubis. It transmits the spermatic funiculus, or (in the female) the round ligament of the uterus, covered by the cremaster muscle or cremasteric fascia. The opening is of considerable extent, and its edges are drawn together by a thin fascia, strengthened superficially by a number of arched and horizontal fibres, called the intercrural fibres, which arise from the inguinal ligament and sweep medially across the cleft in the aponeurosis.

The margins of the ring constitute its crura. The inferior crus is narrow, and is formed from that part of the aponeurosis which joins the pubic tubercle, and is continuous with the medial end of the inguinal ligament. The superior crus is the part of the aponeurosis medial to the ring which is attached to the crest and symphysis of the pubis. It is flat and broad.

The intercrural fibres and the crura of the subcutaneous inguinal ring are continuous with a thin tubular sheath, the intercolumnar or external spermatic fascia, which is attached to the margins of the "ring," and forms an envelope for the

spermatic funiculus or round ligament after they have passed beyond the abdominal wall.

Lig. Inguinale Reflexum Collesi.-The reflexed inguinal ligament of Colles (O.T. triangular fascia), is a triangular band of fibres placed behind the medial superior crus of the subcutaneous inguinal ring. It consists of fibres from the

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FIG. 424. THE LEFT OBLIQUUS EXTERNUS ABDOMINIS

opposite external oblique aponeurosis, which, having traversed the linea alba, to gain an insertion into the crest and tubercle of the pubis.

The obliquus externus muscle is superficial in almost its whole extent. It is overlapped posteriorly by the latissimus dorsi muscle, but may be separated from it just above the iliac crest by an angular interval (trigonum lumbale or triangle of Petit).

M. Obliquus Internus Abdominis.-The obliquus internus abdominis is a broad thin sheet of muscle which lies between the obliquus externus and the

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transversus. It arises from, (1) the lumbo-dorsal fascia, (2) the anterior twothirds of the iliac crest, and (3) the lateral half of the inguinal ligament.

It runs for the most part, upwards and forwards, and its highest fibres are inserted directly into the last three ribs. The rest of the fibres end in an extensive aponeurosis, broader above than below, which splits along the linea semilunaris, to form, along with the aponeuroses of the obliquus externus and transversus muscles,

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SERRATUS
ANTERIOR

LATISSIMUS
DORSI

OBLIQUUS

EXTERNUS

ABDOMINIS

(reflected)

OBLIQUUS INTERNUS
ABDOMINIS

APONEUROSIS OF OBLIQUUS EXTERNUS (reflected)

APONEUROSIS OF OBLIQUUS INTERNUS

APONEUROSIS OF OBLIQUES EXTERNUS (reflected)

CREMASTER MUSCLE

Suspensory ligament

of penis

Spermatic funiculus

FIG. 425.-THE RIGHT OBLIQUUS INTERNUS ABDOMINIS.

the sheath of the rectus abdominis, and is inserted into the seventh, eighth, and ninth costal cartilages, and into the linea alba from the xiphoid process to the symphysis pubis. The fibres arising from the inguinal ligament join with those of the transversus muscle having a similar origin to form the falx aponeurotica inguinalis (O.T. conjoined tendon), which passes altogether anterior to the rectus muscle, to be attached to the pubic crest and tubercle, and to the ilio-pectineal line.

The obliquus internus is limited above by the inferior margin of the thorax

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