OF DIDELPHYS VIRGINIANA. 105 



with the anterior crural nerves to the outside. The insertion of Poupart's ligament is 

 rigidly defined ; it is into the inner aspect of the extreme point of the outer prong of the 

 base of the marsupial bone, just opposite the origin of the pectineus. This narrow, distinct, 

 glistening tendon forms the outer "pillar of the ring." The "ring" is of large size, and pyr- 

 iforni or elliptic contour, its broadest part uppermost. About an inch from the insertion of 

 the tendon, the fibres curve away from its border, overarching the ring, and descending again 

 on the inner side nearly or quite to the base of the marsupial bone, forming the "mesial 

 pillar." The contour of the ring is well marked ; an "intercolumnar fascia" closes the open- 

 ing ; the spermatic cord enters at its lower corner. After forming the mesial pillar, the 

 aponeurosis is firmly attached to the whole length of the marsupial bone, as it passes over 

 the outer surface of the latter to proceed to its final insertion into the linea alba and sym- 

 physis pubis. The muscle is thick and fleshy as far as the outer border of the rectus, 

 where it becomes aponeurotic, and closely invests the rectus, as far down as the beginning of 

 the pyramidalis, after which it lies directly upon the latter. In the inguinal region it be- 

 comes aponeurotic along an imaginary line drawn from the top of the ilium to the top of 

 the marsupial bone. All but the most superior and anterior of its fibres pass almost di- 

 rectly downward. 



Ohllquus interims. — This muscle is much smaller than the preceding, as well as thinner ; 

 its superficies equals that of the abdomen alone. It arises fleshy from the greater part of 

 Poupart's ligament, and from the apex of the ilium, and, by an aponeurosis common to it 

 and the transversalis, from the lumbar f\xscia. The lower border is fleshy, and stretches 

 nearly horizontally inward from Poupart's ligament to the upper part of the marsupial bone, 

 a stout bundle of fibres being inserted into the tip of that bone. The rest of the muscle 

 passes more and more directly upward, till its posterior part is vertical. Its anterior mar- 

 gin ends along a " linea semilunaris " by blending its aponeurosis with that of the trans- 

 versalis. This termination of the fleshy fibres is along a straight, oblique line from the tip 

 of the marsupial bone to the most dependent point of the tenth rib. From this line inward 

 no separate aponeuroses for internal oblique and transversalis can be demonstrated ; and 

 the same is the case with the lumbar aponeurosis back of a line from the tip of the ilium 

 to the last rib, though it is presumable that two fibrous layers enter into the composition 

 of these aponeuroses. The costal insertion of the muscle is by three or four fleshy digita- 

 tions into as many of the lower ribs. 



Transversalis. — Except for a small space, as noted below, this muscle is fleshy through- 

 out. It arises flisciculate from the inner surfaces and costal interspaces of all the floating 

 ribs, interdigitating with the diaphragm ; the lumbar aponeurosis of origin is formed by 

 coalescence of two layers enclosing the quadratus; upon which, and upon blending with 

 the border of the internal oblique, the muscle becomes fleshy. It is attached fleshy to the 

 top of the ilium; its lower fleshy border is not directly continuous with the cremaster, so 

 that the latter does not appear, as in some animals, as a direct scrotal prolongation of the 

 transversalis ; but is separated from the latter, more or less perfectly, by an areolar inter- 

 val, and may usually be traced to the ilium itself. The transversalis, thickest above, is 

 everywhere transverse in the direction of its fibres, the uppermost of which overlie the 

 xiphoid cartilage ; and along the upper two-thirds or three-fourths of its length fleshy fibres 

 reach the linea alba. There is no splitting of the aponeurosis to get outside the rectus 

 below ; near the point where the muscle passes outside the rectus in the human subject, 



MEMOIRS BOST. SOC. SAT. niST. VOL. II. 27 



