Such is unquestionably the usual mode of insertion of the tendon of the transversalis muscle ; but Mr. Guthrie has lately called the attention of anatomists to a variety which it is important to know, although it cannot be of frequent occurrence. In this variety the spermatic cord appears to pass through a slit in the inferior margin of the transversalis muscle, so that a bundle of muscle passes behind as well as before the cord ; the posterior one end ing in tendinous fibres, which, like the folded fibres above described, are inserted into Pou part's ligament."' It is very generally believed that the inferior fibres of this muscle contribute, as well as those of the obliquus internus, to form the cremaster. The two muscles are so closely connected externally by their inferior margins, that it is natural to suppose that both do send fibres to the cremaster. Sir Astley Cooper expresses the relation of the cremaster to these two muscles in the clearest way, when he says that it arises from Poupart's ligament within the inguinal canal, and there blends with some of the fibres of both these muscles.t A thin layer of cellular tissue covers the transversalis muscle, and separates it from the obliquus internus. At its superior margin it is intimately related to the diaphragm, and some of its fibres seem to be continuous with it : posteriorly, by the triple partition of its tendon, it ensheaths the lumbar muscles, and it lies upon the fascia transversalis, which, with a layer of cellular tissue, separates it from the peritoneum. I 4. Rectus abdominis ( sterno-pubien). After the superficial fascia has been removed so as to expose the aponeurosis of the external ob lique, the recti muscles are seen on either side of the middle line covered by this aponeurosis, which it is necessary to slit up in order to ex pose the muscles. The rectus owes its name to the perpendicular course of its fibres, which pass from the pubis to the thorax, nearly parallel to the middle line. It is long and narrow ; however, its breadth increases as it advances upwards, and as it increases in breadth it diminishes in thickness. At the pubis the muscle has its most fixed point of attachment, whence it is generally said to have its origin there : it , arises by a short tendon from the symphysis of the pubis; this tendon is very narrow at its origin, but soon expands, and unites with the muscular fibres, which pass vertically upwards to the lower margin of the thorax, where the muscle considerably increased in breadth, and divides into three portions ; the first or internal one is inserted into the costoxiphoid ligament and cartilage of the seventh rib ; the middle, larger than the preceding, into the cartilage of the sixth rib at its inferior edge and anterior surface ; -and the external, the largest of the three, into the inferior edge of the cartilage of the fifth rib. This muscle is remarkable for its tendinous intersections, which cut the fibres at right angles, and are called linea transverse ;$ they vary in number from three to five, and are always more numerous above than below the umbilicus. In general there is one on a level with the umbilicus ; the superior one being about an inch below the superior attachment of the muscle, and a third midway between these two : when a fourth and a fifth exist, they are below the umbilicus. They adhere to the an terior wall of the sheath closely, and but very slightly or not at all to the posterior. Some times the intersection does not go completely through the thickness of the muscle so as to appear on its posterior surface, and thus the posterior fibres are longer than the anterior.; but as Bichat remarks, it never happens that any of the muscular fibres pass from one extre mity of the muscle to the other without uniting at least one of these intersections. Sometimes, too, the intersection does not go through the breadth of the muscle, and this is generally the case with that below the umbili cus. The effect of these intersections is to convert the muscle into so many distinct bellies, each of which has its proper action, and is, as Beclard asserts, provided with a separate --nerve.f The rectus muscle is enveloped in a fibrous sheath, the mode of formation of which the reader must have collected from the description of the oblique muscles. The anterior wall of this sheath is formed by the aponeurosis of the external oblique alone over the chest, and by the same aponeurosis and the anterior layer of that of the internal oblique, from the xiphoid cartilage to the inferior fourth of the muscle ; (both which aponeuroses over the internal half of the muscle are so adherent to each other as to form but one lamina;) and in its inferior fourth by the conjoined aponeuroses of the two obliqui and transversalis.
The posterior wall of the sheath is deficient superiorly where the muscle covers the carti lages of the ribs with which it is in contact, and inferiorly for a space corresponding to the inferior fourth of the muscle. So much of it as exists is formed by the tendon of the transver salis and the posterior lamina .of that of the internal oblique, so that the rectus appears to have passed at its inferior extremity through a transverse slit in these conjoined tendons, so as to get between them and the peritoneum.
The rectus muscle covers, at its superior ex tremity, the cartilages of the two last true ribs and a part of those of the two first false, and also the xiphoid appendix. The internal mam mary and epigastric arteries are found behind it in the sheath.
Between the recti muscles is the fibrous cord called linea alba, produced by the interlace ment of the aponeuroses of the opposite sides, noted in surgery as being in its inferior half the seat of the operations of paracentesis abdominis, paracentesis vesicm supra pubem, the supra pubic lithotomy, and the Caesarean operation. This cord extends from the xiphoid cartilage to the symphysis pubis, with the anterior liga ment of which articulation it is identified. - It does not present the same breadth in its whole course, being broader in the umbilical region than elsewhere. In this region we find in the linea alba the perforation which gave passage to the umbilical vessels in the foetus and the urachus, and through which the fibrous remains of those vessels pass to be inserted into the skin, whereby is formed the cutaneous depres .sion which marks the situation of this opening. In the adult the umbilicus may be considered as a point of considerable strength ; in the esti mation of some it is the strongest point in the abdominal parietes : in dissecting away the skin at this point, we find subjacent to it a very con densed cellular tissue, to which and to the skin the fibrous cords into which the umbilical vessels have degenerated adhere closely; these cords, too, adhere not .only to the skin, but likewise to the margin of the fibrous ring through which they pass. " The umbilical opening, therefore," says Scarpa, " in the infant two months after birth, and still more in the adult, is not only like the other natural openings of the abdomen, strength ened internally by the application of the peri toneum and of the cellular substance, and on the outside by the common integuments, but it is likewise plugged up in the centre by the three umbilical ligaments and by the urachus; these ligaments form a triangle, the apex of which is fixed in the cicatrix of the integuments of the umbilicus, the base in the liver, in the two ilio-lumbar regions, and in the fundus of the urinary bladder; by this triangle is formed a strong and elastic bridle, capable of itself alone of opposing a powerful resistance to the viscera attempting to open a passage through the aponeurotic ring of the umbilicus, which apparatus does not exist at the inguinal ring or femoral arch."* . In the foetus the ring of the umbilicus is proportionally larger than at any period after birth when the cicatrix is fully formed : it is, however, at the full term, or even at the seventh or eighth month, and in the healthy state of the parts, equally filled up by the umbilical vessels and urachus, and we would say is equally capable of resisting intestinal protusion as at any subsequent period. Hence it may be in ferred that congenital umbilical ruptures are always of very early date, being attributable to the persistence of the opening at the umbilicus, and the continuance in it of the intestinal pro longation which exists there naturally at a very early period. It may likewise be inferred that the rupture in the adult can much more easily occur in the vicinity of, than through the umbi lical ring; and experience confirms this deduc tion from the anatomy of the parts.