ANATOMY OF THE HORSE. 
363 
formation of the abdominal parietes, laterally and interiorly, give 
great support to the contained viscera. In action, they compress 
the bowels; arid, in that manner, assist both in the evacuation of 
the faeces and urine, and also in the expulsion of the foetus. At 
the same time, they will have the effect of diminishing the cavity 
of the chest, in the longitudinal direction, by forcing the abdomi¬ 
nal viscera against the diaphragm, and driving that muscle for¬ 
wards into the form of a convexity; and in the transverse as 
well, though not in the same degree, by compressing and retract¬ 
ing the ribs. But, in almost all their operations, they are con¬ 
nected with the diaphragm ; and, together with it, produce effects 
that can only be understood by studying their separate and com¬ 
bined actions. 
obliquus internus ABDOMINIS.— (Ilio-abdominalis.) 
Situation . —Postero-lateral and inferior parts of the abdomen. 
Form. —Broad; thin; fan-shaped. 
Attachment .—Outwardly and posteriorly, to the spine of the 
ileum, from which the fleshy fibres radiate : inwardly, at the linea 
semilunaris, it becomes tendinous, and inseparably united with 
the aponeurosis of the external oblique ; along with which it is 
continued to the linea alba. 
Relations .—Externally, with the former muscle; internally, 
with the transversalis and rectus. 
Di rection .—Radiated : the superior fasciculi being directed 
towards the cartilages of the ribs ; the inferior, towards the linea 
alba : both decussating those of the external oblique. 
Structure .—Fleshy, from the ileum to the linea semilunaris : 
afterwards, to its termination, an expanded and loose-textured 
tendon. 
Action .—These muscles will aid the former in sustaining the 
weight of the viscera, as well as in compressing them : they will 
have a more partial effect in the expulsion of the faeces and urine, 
in consequence of being placed farther back than the preceding. 
In any action the oblique muscles may have in turning the body 
to one side, the right internal oblique wall co-operate with the 
left external oblique, and vice versa . 
transversalis abdominis. — (Lumbo-abdominalis.) : 
Situation .—Inferior and lateral parts of the abdomen. 
Figure .—Broad; flat; quadrilateral: broader posteriorly than 
anteriorly. 
Attachment .—Anteriorly, to the inner surfaces of the cartilages 
of all the false ribs ; superiorly, to the transverse processes of the 
