In some female subjects we see an arrange ment of the inferior fibres of the internal oblique as they cross over the round ligament, which resemble a rudimentary state of the cremaster muscle.
A thin layer of cellular tissue, sometimes containing a small quantity of fat, is interposed between the anterior surface of the obliquus internus and the obliquus externus. At the infe rior edge of the obliquus internus the spermatic cord is seen emerging from the abdomen and passing obliquely inwards and a little down wards to the external abdominal ring. Here it lies in a groove or channel, called the inguinal canal, which extends from the point at which the spermatic cord emerges from the abdomen,(the opening in the fascia transversalis called in ternal abdominal ring) to the external abdo minal ring. This canal is bounded or covered anteriorly by the tendon of the obliquus externus ; posteriorly by the fascia trans versalis and some fibres of the tendon of the transversalis muscle towards the inner side ; superiorly by the margin of the obliquus in ternus and transversalis muscles ; and inferiorly by the groove of Poupart's (A full description of this canal will be found in the article GROIN, REGION OF THE.) 3. Transversalis ( lumbo-abdominal, lumbo ili-abdominal). This muscle is immediately under cover of the obliquus internus ; its name is derived from the transverse direction of its fibres. In its general character it resembles the obliqui, being like them a muscular lamella, inserted into a tendinous expansion, which again is inserted into the linea alba. Supe riorly the fleshy fibres of this muscle are attach ed by distinct bundles to the internal surface of the cartilages of the ribs forming the lower margin of the thorax, where these bundles in digitate with those of the diaphragm : 2dly, in the interval between the last rib and the crista ilii, the fibres arise from a tendinous lamella, which itself is trifoliate in its origin. This ten don is found as an undivided lamella between the outer margin ofthe quadratuslamborum and the commencement of the fleshy fibres of the muscle, extending vertically from the last rib to the crista ilii. ( Fig. 4, /.) The three laminae of which this tendon is composed arise from different portions of the vertebrae in the lumbar region of the spine ; the posterior, which is thick and strong, and is commonly called fascia lumborum, arises from the extremities of the spinous processes, and covers the lum bar mass of muscles. ( Fig. 4, g.) The mid
dle, which is weak, is attached to the apices of the transverse processes ; it lies in front of the lumbar mass and behind the quadratus lumbo rum (fig. h ); and the anterior arises from the pedicles which connect the transverse processes to the bodies of the vertebrae, and covers the quadratus lumborum muscle in front (fig. 4, j). Inferiorly, the transversalis muscle at taches itself to the inner lip of the crista ilii for its three anterior fourths, and to the ex ternal third or half of Poupart's ligament, cor responding to the attachments of the obliquus internus. The fleshy fibres of the muscle pass from these several points of attachment trans versely inwards, the middle being the longest, and the superior the shortest, and are in serted into the outer convex margin's of a tendinous aponeurosis, which extends to the linea alba. This aponeurosis is intimately connected with the posterior division of that of the obliquus internus for an extent corre sponding to the three superior fourths of the rectus muscle, behind which both pass to be inserted into the ensiform cartilage and linea alba, (fig. 4, a,) forming the posterior wall of the sheath of the rectus. Inferiorly, as we have already remarked, these conjoined tendons go together in front of the rectus, and are inserted into the inferior fourth of the linea alba and into the pubis. At the inner extre mity of the ingiiinal canal, it will be seen by carefully raising up the spermatic cord, that this union of the tendons of these two muscles ceases, and we can trace the fibres of the trans versalis tendon passing down in a curved direc tion, more curved as they are more external, and insinuating themselves behind the cord to be inserted into Gimbernat's and Poupart's ligament for about its external third or fourth. This mode of insertion of the transversalis ten don was first-described by Sir Astley Cooper,t and these fibres were by him called the folded fibres of the transversalis. They adhere to the subjacent fascia, (fascia transversalis,) and add to the strength of the inner portion of the pos terior wall of the inguinal canal. They cor respond, in a great measure, to the external abdominal ring, and may be counted as one of the obstacles provided against the direct descent of a hernia.