Inferiorly, the abdominal wall is supplied by two considerable and very constant arteries, viz. the epigastric, which may be distinguished from the artery that supplies the integuments by the appellation deep, and the circumflexa The epigastric artery arises in general from the external iliac a little way above Poupart's liga ment; it at first inclines downwards to that ligament, and then turns upwards, and directs itself forwards and inwards, crossing the iliac vein; it then runs along the posterior surface of the anterior wall of the abdomen, inclosed be tween the peritoneum and fascia transversalis, at first situated between the external and inter nal abdominal rings, and on arriving at the rectus muscle, the sheath of which it enters about two inches above the pubis, it gives of branches from either side to the abdominal muscles and peritoneum, and behind the linea alba, establishes a very free inosculation with its fellow of the opposite side. As it lies behind the inguinal canal, the epigastric artery is much nearer to the internal than to the external abdo minal ring, being to the pubic side of the former ; here the vas deferens, as it passes up from the pelvis to the inguinal canal, books over it, and receives one or two small branches from it. In passing to the rectus muscle, this artery lies internal to the linea semilunaris. It enters the sheath of the rectus, and then termi nates by anastomosing with the internal mam mary. The course of this artery demands par ticular attention from the surgical anatomist in reference to the operations for inguinal herniae, and to that for paracentesis abdominis, when the abdomen is perforated in the linea semilu naris. The trunk of the artery is so distant from the linea alba in its whole course, that it is free from danger in any operation performed in that line,- or in the internal half of the rectus muscle, and its security in such operations is increased under the altered state of parts con sequent on pregnancy, ascites, or any abdomi nal tumour pressing similarly on the abdominal wall. In these cases the distance of the artery from the linea alba is increased by the flattening of the rectus muscle, which results from its compression. — (See GROIN, REGION OF; HERNIA; ILIAC ARTERY.) The circumflexa ilii artery comes likewise from the external iliac, near to the origin of the epigastric; it passes upwards and outwards to wards the spine of the ilium, runs along the line of junction of the fascia iliaca with the fascia transversalis, covered by the fascia, and follows the circumference of the iliacus internus muscle to end in anastomosing with the iliolum bar artery. From that part of the artery which intervenes between its origin and the spine of the ilium, come the principal branches which it supplies to the abdominal muscles.
The lateral and posterior walls of the abdo men are supplied by the inferior intercostals, the lumbar, the iliolumbar, the circumflexa ilii arte ries; the superior walls by the phrenic branches of the internal mammary and by those of the aorta. It is in cases where the aorta has been obliterated that we can see best the extent of arterial ramification on the abdomen, and can appreciate the benefit of these numerous anas tomoses, and the connexion which they esta blish between the upper and lower portions of the aorta.* b. The veins.—The veins of the abdominal parietes are much more numerous than the arteries ; each artery has its accompanying vein or veins, but those which are especially de serving of attention are the tegumentary veins which accompany the superficial epigastric artery, and those which ramify along with the deep epigastric and mammary. The subcuta neous veins demand attention in consequence of the considerable size which they sometimes attain; this enlargement is commonly attendant on ascites and on pregnancy, and is occasionally, to a remarkable extent, a consequence of some irregularity, obstructiont or retardation of the circulation, in the deep-seated veins of the ab domen, more especially the inferior vena cava. The veins which accompany the superficial epigastric artery empty themselves by one or more trunks into the vena saphena at the upper part of the thigh.
Two veins generally accompany the deep epigastric artery, which empty themselves into the external iliac vein. These veins are equally
subject to enlargement with the preceding, and from similar causes, and they are often found in a varicose condition in women who have borne many children.
Some curious anomalies have been observed in the venous circulation of the anterior abdo minal wall, which, as being calculated to in terfere with the operator, the practitioner would do well to note. M. Meniere* has described a case in which a very large vein, arising from the external iliac, passed up along the linea alba to the umbilicus, was continued along the obliterated umbilical vein, and opened into the vena portw. In another case, recorded by the vein originated in the same manner by two roots, reached the umbilicus, taking a course parallel to the umbilical artery, formed an arch outside the navel, and having re-entered the abdomen, opened into the vena portze. In another instance which occurred to Cruveilhier the superficial veins in the hypogastric region were enormously enlarged, at the umbilicus they ended in a trunk as large as a finger, which communicated with the vena cava as it passed under the liver.t Berard proposes to explain, by the supposition of the existence of such anomalies as those above described, the occurrence of fatal hemorrhages from wounds inflicted at the umbilicus, which have been attributed to the persistence of the um bilical vein.X c. The lymphatics.—Those on the anterior wall communicate above with the axillary glands, and below with those of the groin : the deep-seated lymphatics of the posterior wall communicate with the glands which lie along the lateral and anterior surfaces of the lumbar spine.
d. The nerves.—The nerves of the abdo minal parietes are derived from the inferior intercostals and from branches of the lumbar plexus. The seventh, eighth, ninth, tenth, eleventh, and twelfth intercostal nerves termi nate in supplying the transverse and oblique muscles and the recti ; the twelfth lies in front of the quadratus lumborum muscle, and gives several filaments to that muscle. The ilio scrotal and inguino-cutaneous nerves are the branches of the lumbar plexus which mainly. supply the inferior part of the oblique and transverse muscles. One branch of the genito crural, which is found in the inguinal canal, also sends some twigs to these muscles.
The posterior wall is supplied by the sub divisions of the posterior branches of the lumbar nerves.
Physiological action of the abdominal parietes and muscles.—We have already alluded to the peculiarity which distinguishes the abdominal cavity when compared with the other great cavities, namely, that its walls are in greatest part composed of contractile tissue. At first view the muscular apparatus of the abdomen would appear to be a great constrictor muscle destined principally to exert its influence on the cavity and its contents ; but when we take into account the attachments of those muscles to the ribs, the vertebrae, and the pelvis, it becomes evident that they must likewise be destined to act upon the thoracic and pelvic cavities, as well as upon the vertebral column. In the constitution of the abdominal parietes we observe, as Berard* remarks, the most happy adaptation of structure to uses. A completely osseous covering would have greatly interfered with the functions of the abdominal organs, which are liable to experience changes both extensive and often very rapid, either by reason of the introduction of alimentary matter, whether solids or fluids, or by the disengage ment of gases within the digestive tube, or by the progressive development of the impregnated uterus. We may moreover add that an exact repetition of the structure of the walls of the thorax would not have been well adapted to the abdomen for the same reason, namely, the too great resistance which it would afford to compression from within, thereby interfering with the distensibility of the enclosed viscera. The resistance, too, which a wall so constituted would afford to impulses from without could not have been so easily adapted to the impetus of the forces likely to act upon them as a purely muscular wall whose contractions and the intensity of them are obedient to the will.