Psoas parvus, (prelombo-pubien). This muscle is similar to the psoas magnus in course and position. It is very much elongated, its fleshy portion being small and tapering. Su periorly it is attached to the body of the first lumbar vertebra, and to the intervertebral sub stance between it and the last dorsal, and sometimes to the body of the last dorsal ver tebra. The fleshy belly soon ends in a flattened tendon, which descends obliquely downwards and outwards over the anterior surface of the psoas magnus, and at its inferior extremity ex pands considerably, and is inserted along the linea ilio-pectinea near the junction of the ilium and pubis. An expansion from the margins of this tendon becomes united on the outside to the fascia iliaca, and on the inside to the internal portion of the same fascia which covers the great psoas, and passes beneath the iliac vessels to become united at the brim of the pelvis to the pelvic fascia.
We must not omit to state that the crura of the diaphragm, as they descend over the bodies of the lumbar vertebra, (see may be regarded as entering into the formation of the posterior wall of the abdomen. The inferior wall of the abdomen is not devoid of muscle, although those muscles can exercise very little, if any influence upon the contents of the cavity. The iliac fossa affords a large surface for the attachment of one of the principal muscles connecting the thigh with the trunk. This muscle is named Iliacus internus, (iliaco-trochanterien.) This muscle fills up the iliac fossa, to the whole of whose concavity as well as to its margin, and the two anterior spinous processes of the ilium and the interval between them, its fibres are attached. From these several points of origin the fibres converge to form a thick and broad belly, which passes over the upper part of the acetabulum and horizontal ramus of the pubis, filling up the external portion of the space between that bone and Poupart's ligament; and it is inserted, as we have already observed, into the outer margin of the tendon of the psoas magnus, which is for that reason gene rally described as the common tendon of the psoas and iliacus. The anterior surface of this muscle is traversed by two of the external branches of the lumbar plexus (inguino-cuta neous), and the anterior crural nerve passes between its internal margin and the psoas magnus.
The superior wall of the abdomen is entirely formed by the muscular vault of the diaphragm, which by its contraction and relaxation exer cises a considerable influence on the abdominal contents,and causes very obvious changes in the form of the cavity. The concavity of this vault is towards the abdomen, and is greater on the right side than on the left, in consequence, as it is said, of the presence of the liver on that side. It is through the several openings in this wall that a communication is established be tween the thorax and abdomen. The largest of these openings are, that on the right side, which is completely tendinous, for the passage of the vena cava; the opening for the (eso phagus; and that for the aorta ; in addition to these there is a small one behind the centre of the xiphoid appendix formed by a divarication of the anterior fibres of the dia phragm, through which the cellular tissue of the anterior mediastinum communicates with the abdominal subserous tissue. There are,
moreover, openings for the transmission of the splanchnic nerves, and the continued trunks of the sympathetics, as well as of branches of the phrenic arteries and nerves, and the abdominal branches of the internal mammary. The par ticular description of this muscle will be given under the article DIAPHRAGM.
4. The next element which enters into the formation of the abdominal parietes is a fibro cellular expansion, which, varying in density in different situations, lines the whole internal surface of the muscular walls. It is strongest and exhibits most of the real fibrous character in the iliac region on the anterior wall, and over the iliac fossa in the inferior. In the former situation it has received the name of fascia transversalis, which was applied to it by Sir A. Cooper in consequence of its close con nexion with the transversalis muscle : in the latter, it is called the fascia iliaca, from its connexion with the iliac fossa and muscle.
The fascia transversalis is best seen by re moving the muscles which lie anterior to it : it is then distinctly observed to extend from the outer margin of the rectus muscle internally over the posterior surface of the anterior wall of the abdomen, and gradually to assume the character of a thin but condensed cellular la mella over the abdominal surface of the lateral wall : it may, however, be traced internally as far as the linea alba behind the rectus muscle, but here it is extremely thin, and has totally lost the fibrous character. Inferiorly this fascia adheres to Gimbernat's ligament and to the reflected margin of Poupart's, from which it is said, by some French anatomists, to originate. Along the line of Poupart's ligament and ex ternal to it along the crista ilii, this fascia is united with the fascia iliaca, the union be ing indicated by a white opaque line formed by a thickening of the membrane, taking the course of Poupart's ligament and the crista except where it is interrupted for the passage of vessels or other parts. Superiorly, the fascia transversalis also degenerates into a cellular lamella, which passes on the transversalis muscle to the diaphragm. It is for a short distance above Poupart's ligament that this fascia demands most attention; here it forms the posterior wall of the inguinal canal, and at a point a little external and superior to the middle of Poupart's ligament it presents an opening or separation of its fibres, through which the sper matic vessels and vas deferens united by lax cellular tissue pass into the inguinal canal, carrying around them a funnel-shaped mem brane which seems to be a prolongation from or continuation of the margins of this opening, but which is in texture merely a condensed cel lular layer. This prolonged membrane is the first covering which the spermatic cord receives upon its formation, which takes place as its several constituent parts meet at the opening or slit in the fascia transversalis ; it immediately invests the cellular tissue connecting these parts, which is the tunica vaginalis of the cord ; as it proceeds, the cremaster muscle adheres to it from the external oblique and transversalis muscles, and this again receives at its exit through the external abdominal ring another cellular expansion, to which we have already alluded.