364 
ANATOMY OF THE HORSE. 
lumbar vertebrae; posteriorly, to the anterior spinous process of 
the ileum: inwardly, to the entire linea alba. 
Relations. —On the outer side, with the internal oblique and 
straight muscles : on the inner side, with the faschia transversalis 
and peritoneum. 
Direction. —Transverse, directly across the abdomen. 
Structure. —Partly fleshy; partly tendinous : the tw o sub¬ 
stances divided by the semilunar line, w hich leaves the tendinous 
part broad, posteriorly; the fleshy, anteriorly. 
Action. —These muscles will assist the oblique in supporting 
the burden of the viscera, and are more advantageously placed 
to effectually compress them: they are consequently doing more 
in the complete evacuation of the bow r els. 
rectus abdominis.— (Sterno-pubialis.) 
Situation. —Infero-median part of the abdomen. 
Form. —Elongated; flattened from above downwards : broader 
in the middle than at either extremity. 
Attachment .—Anteriorly, to the cartilages of the six or seven 
posterior true ribs; and to the sternum : posteriorly to the pubes, 
near its symphysis. 
Relations. —Anteriorly, it is placed between the pectoralis ma¬ 
jor and the cartilages of the ribs; externally, it has the united 
tendons of the external and internal oblique; internally, that of the 
transversalis: also, the internal pectoral and epigastric arteries ; 
and the faschia transversalis and peritoneum. 
Structure. —Tendinous at its attachments : the anterior one is 
aponeurotic. The intermediate length is fleshy, but divided into 
portions by about a dozen transverse tendinous interlacements or 
intersections. Each muscle, by itself, is inclosed within a sheath, 
formed of the united tendons of the external and internal oblique 
muscles, inferiorly; and of that of the transverse muscle, supe¬ 
riorly. At the places where the tendinous bands exist, the sheath 
contracts firm adhesion to the muscle; and it is this union and 
structure that gives rise to the existence of the linea transversalis. 
The recti occupy about one-third of the abdominal superficies. 
Action. —Their principal use appears to be that of bracing the 
middle parts of the belly; and, thereby, counteracting that tenden¬ 
cy to relaxation which must exist from the constant dependence of 
the bowels. They can have but little effect in compressing the 
bow r els ; though they will take some part in contracting the cavity 
of the thorax, by drawing the sternum upwards and backwards. 
Remark. —A careful incision through some of the posterior 
fibres of the transversalis will disclose to view an expansion of 
