2. Obliquus internus (obliques ascendens, ilio-abdominal, ilio-lumbo-costi-abdominal) is smaller than the preceding muscle, which it resembles in shape and general characters. The direction of its fibres, however, is opposite, inasmuch as the fibres of the two muscles decussate with each other, thus adding con siderably to the strength of the abdominal wall, and forming a great protection against visceral protrusions. The external attachments (or, as systematic writers call it, the origin of the mus cle) is 1. by short fleshy fibres to the tendinous expansion covering the lumbar mass of muscles, called fascia lumborum, which is formed by the posterior lamina of the tendon of the trans versalis abdominis : 2. to the two anterior thirds of the middle portion of the crista between the external oblique and the transver salis as far forwards as the anterior superior spine : 3. to the groove in the upper or abdo minal surface of Poupart's ligament for about its external third. The superior fibres pass upwards and inwards, and are inserted by fleshy slips into the cartilages of the twelfth, ele venth, and tenth ribs, in the intervals between which they are either separated from the inter costal muscles by a fibrous intersection, or con founded with them, and by a tendinous aponeu rosis into the cartilages of the ninth, eighth, and seventh ribs as well as into the xiphoid cartilage. Lower down, the fibres which arise from the crista ilii, as well as those from Poupart's liga ment, pass inwards, the superior obliquely upwards and inwards, the inferior more hori zontally, and the lowest fibres inclining a little downwards, and are all inserted, like those of the obliquus externus into the outer convex margin of an aponeurotic expansion, which goes to be inserted along the middle line. This ten don passes inwards for a short distance, nearly as far as the outer margin of the rectus muscle, as a single lamina. Along this margin, and as low down as the inferior fourth of the rectus muscle, the tendon divides into two laminae, of which the anterior adheres to the posterior surface of the tendon of the external oblique, and the posterior to the subjacent tendon of the transversalis, both laminae going to be inserted into the ensiform cartilage and linea alba, the one in front, the other behind, the rectus muscle. (See fig. 4, a.) For a distance, however, corres ponding to the inferior fourth 'of the rectus muscle, the tendon of the obliquus internus re mains undivided, and does not adhere to that of the obliquus externus. It, however, is united, although not inseparably, to the tendon of the transversalis, and both go in front of the rectus to be inserted into the linea alba and pubis : these tendons are here called by some the con joined tendons. Along the line at which the tendon of the obliquus internus divides into two laminae, the aponeurosis of the obliquus externus and that of the transversalis adhere to it more closely than they do externally to that line, and thus a thickened portion of the abdominal aponeurosis is formed, taking the course of the outer margin of the rectus muscle : this line is called the linea senzilunaris, and is that in which the operation of paracentcsis abdominis used formerly to be practised.
The inferior margin of the obliquus internus is deserving of particular attention. The in ferior fibres attached to the external third of Poupart's ligament in the groove formed in it pass transversely inwards and parallel to the ligament, crossing over the spermatic cord, to be inserted into the pubis. Here the muscle is confounded with the inferior fibres of the sub jacent one, the transversalis ; so that it is not only difficult to say which muscle passes low est down, but it is difficult, and often impossible, to separate the two muscles. Hence the lower margins of the fleshy fibres as well as of the apo neuroses of these two muscles are constantly spoken of conjointly; however, I have several times succeeded in separating them distinctly, and I am decidedly of opinion that the apo neurosis of the obliquus internus seldom or never descends so low down as that of the trans versalis. The lowest of the fibres of the obliquus
internus are sometimes observed to separate a little from the others, so as, instead of a directly transverse, to assume a course slightly curved with the concavity upwards and a little outwards, lying in front of the cord ; in some cases fibres of this kind are observed to lie in front of the spermatic cord, and to descend much lower down, taking of course a much more curved direction, still attached on the outside to Pou part's ligament, and on the inside to the pubis, so that a series of curved fibres are thus found to adhere to the anterior surface of the cord and of the tunica vaginalis, exhibiting an equal num ber of reversed arches. But this disposition is rarely seen in its most highly developed state, excepting where some tumour has been con nected with the cord or testicle, as hernia, hydrocele, &c.
This arched arrangement of muscular fibres in connection with the spermatic cord and tunica vaginalis testis constitutes the Cremas ter muscle (xcp,aw, suspendo,) the great tenuity of which in the natural state of the parts has ren dered it difficult to determine its precise attach ments, and consequently has given rise to the great discrepancy which is observable between the descriptions of different writers. When this muscle is examined in a case of old hernia or hydrocele, it is found, as Scarpa originally described it, to consist of two bundles ; the first, external to the cord which arises from Poupart's ligament alongwith the internal oblique, follows the course of the spermatic cord, which it ac companies through the external abdominal ring, sending at intervals fibres arching in front of the cord to join a similar bundle on the inner side, as may be seen in the accompanying en graving from a plate in Sir A. Cooper's work on the testis (fig. 3). Inferiorly, this bundle, a good deal diminished in size, crosses over the inferior and anterior portion of the tunica vagi nalis testis, and begins to ascend along the inner side of the testicle and cord, keeping more pos teriorly : this constitutes the second bundle ; it gradually increases in size as it ascends by re ceiving the transverse fibres from the bundle of the opposite side, and it is inserted, sometimes by a distinct tendon, into the pubis near its spine. In some cases I have totally failed, even after the most careful dissection, in detecting a conti nuity by muscular fibre between these two bun dles, insomuch as to lead me to imagine that they may be connected by a very condensed cel lular tissue or thin aponeurotic lamella after the manner of the digastric muscles. In general the external bundle is larger than the internal, but Cloquet has seen the reverse three times; and on referring to my notes, I find I have seen two instances in which the internal bundle exceeded the external in size.
Many anatomists have noticed only the ex ternal bundle of the cremaster, and altogether overlooked its reversed arches, which is not to be wondered at when we remember that even where the lateral bundles are strong and well developed, the arched fibres are sometimes pale and thin. However, the description now given is pretty generally admitted as the true one, and is sanctioned by such observers as Scarpa, Cloquet, Cooper, Velpeau, and I may add that I have seen this arrangement in cases where both testicle and cord were healthy. It would appear that its formation is effected by the testicle in its descent, for before that takes place the muscle does not exist; at least such is the result of Cloquet's observations on a con siderable number of foetuses before, during, and after the descent of this organ. Before the de scent the gubernaculum testis occupies the inguinal canal, and is covered by the fibres of the internal oblique, which adhere to it : when the gubernaculum is drawn down, these fibres descend with it, forming a series of reversed arches.