362 
ANATOMY OF THE IIORSE 
Attachment .—Anteriorly, by fleshy digitations, to the posterior 
borders of the fourteen hinder ribs, below their middles; posteri¬ 
orly, by tendinous fibres, to the two anterior thirds of the crista 
ilei, and to the anterior spinous process; superiorly, to the 
faschia lumborum; and inwardly, through the medium of its 
tendon, to the linea alba, throughout its entire extent. 
Relations. — Externally, with the panniculus carnosus and pec- 
toralis magnus ; internally, with the hinder ribs and their carti¬ 
lages, and with the obliquus internus and rectus; anteriorly, it 
digitates with the serratus magnus. 
Direction .—Oblique: from before, backward; and from 
above, downward. The anterior fibres deviate but little from the 
horizontal line; in regard to the others, their obliquity increases 
from before backwards. 
Structure .—The entire muscle is covered by a dense tendinous 
expansion, named the aponeurosis of the internal oblique muscle , 
which adheres to the fleshy parts through the connection of a 
delicate cellular tissue, intercepted in places by small slips of ten¬ 
don. At the linea semilunaris, however, where the tendon com¬ 
mences, the aponeurosis contracts an almost inseparable adhesion 
to it, accompanying it, thus intimately united, to its termination. 
Towards the flank, the aponeurosis seems to degenerate into 
cellular texture. 
The superior and outer parts of the muscle itself are fleshy 
and digitated; the inferior and inner parts are tendinous and 
aponeurotic. The fleshy part grows broader, but becomes thin¬ 
ner in substance, posteriorly. 
Remarks .—In the flank, the tendon splits into two portions, 
which separate, having a triangular space or opening between 
them, whose cavity is obscured with fat and cellular substance. 
One division of the tendon is a strong band, which is extended 
and expanded upon the inner side of the thigh ; the other por¬ 
tion runs to the ileum, and thence is continued across to the 
pubes: corresponding in its arrangement and structure to the part 
called Poupartfs ligament in human anatomy, though by no 
means well defined in the horse. The triangular aperture between 
these divisions of tendon, which opens into a sort of pouch, closed 
by the union of these tendons on the outer side, but open towards 
the pubes, is the abdominal ring: through it, in the male, passes 
the spermatic chord, from the abdomen into the pelvis; in the 
female, the round ligament passes through it. The aponeurosis 
is considerably strengthened at this part by some additional ten¬ 
dinous fibres, which run transversely from the linea alba towards 
the ileum. 
Action. —This pair of muscles, in contributing largely to the 
