o94 THE HORSE. 
3. Near the edge of the rectus muscle commences the linea semilunaris, 
which marks the union of the fleshy and tendinous portion of the external 
oblique. 
OBLIQUUS ABDOMINIS EXTERNUS is situated on the lateral parts of the 
belly. Origin—hby fleshy slips from the fourteen hindermost ribs, where 
it indigitates with the serratus magnus and latissimus dorsi, and from 
the fascia lumborum, reaching to the antero-superior spinous process 
of the ilium, Jnsertion—tendinous into the whole length of the linea 
alba, and by two strong divisions into the os pubis, between which is 
formed the triangular space called the external abdominal ring. The 
posterior of these, stretching from the ilium to the os pubis, is called 
the crural arch, and corresponds with Poupart’s Ligament in human 
anatomy. Action—it flexes the pelvis on the thorax, and has the power 
of contraction, and, by this means, of expelling the feces, and in the 
mare the foetus ; it also serves to force up the diaphragm, and thus to aid 
in expiration. ; 
OBLIQUUS ABDOMINIS INTERNUS lies deeper than the foregoing muscle. 
Origin—from the transverse processes of the lumbar vertebre and 
antero-inferior spinous process of the ilium and crural arch. J/nsertion 
—to the inner surface of the cartilages of the three or four last ribs, 
and to the ensiform cartilage; also in close union with the tendon of 
the external oblique to the linea alba, Acteon—tu expe: tne feces 
and urine, and to act as above. Like the last, it is also a muscle of 
respiration. ; 
TRANSVERSALIS ABDOMINIS is still deeper than the last-mentioned 
muscle. It has its crigin from the transverse processes of the lumbar 
vertebrae, antero-inferior spine of the ilium, and symphysis pubis. /n- 
sertion—to the inner surface of all the ribs, except the three last, linea 
alba, and ensiform cartilage. Action—to assist the two muscles above, and 
to support the burden of the viscera. 
ReEcTUS ABDOMINIS is placed on each side the median line beneath the 
viscera. Origin—from the symphysis pubis. Jnsertion—to the carti- 
lages of all the ribs, except the three first, linea alba, ensiform cartilage, 
and four posterior bones of the sternum: it blends with the lateralis 
sterni, covering the sides of the sternum. Action—to brace the middle 
parts of the belly, and to contract the thoracic cavity. 
THE PARTS CONNECTED WITH HERNIA formed by the above muscles 
are :—Ist. The umbilicus, which leaves a weak place in the abdominal 
parietes, especially at and soon after birth, through which umbilical rup- 
ture takes place. 2d. The external ring, and the canal of which it is the 
outer boundary, together with the internal ring, which should be carefully 
examined by the student of veterinary surgery. Want of space will, 
however, forbid more than a general description here. ‘The external ring 
has already been described as formed by the posterior tendinous fibres 
of the external oblique, and through this descends the spermatic cord to 
the scrotum. In tracing backwards and outwards this cord to the point 
where it enters the wall of the abdomen, it will be found to lie between 
the fibres of the crural arch and those of the internal oblique, supported 
by the peritoneum and a thin fascia, which is continued from the edge of 
the transversalis muscle, but is not so distinct as the corresponding part 
in the ‘human subject. About three or four inches from the external 
ring this fascia is pierced by the cord, and this part is called the internal 
abdominal ring, the space between the two rings being the inguinal 
canal. (See spermatic. cord, chapter xxii.) 
