DORSAL REGION. 393 
transverse process of the last cervical vertebre. Action—to aid the last- 
named muscles. 
LEVATORES COSTARUM are fifteen or sixteen muscular slips, which con- 
nect the transverse processes of the dorsal vertebrae with the anterior 
borders of the ribs, in the spaces between their tubercles and angles, 
Action—to raise the ribs and enlarge the cavity of the thorax. 
DORSAL REGION. 
Loncissmtus porst hes along the back beneath the muscles of the supe- 
rior extremity (which have been removed). It is a large powerful muscle, 
and forms the chief mass of the soft parts constituting the loins and back. 
Origin—tfrom the crest of the ilium, side of the sacrum, and spinous and 
transverse processes of all the lumbar vertebra. Jnsertion—to the angles 
of the twelve posterior ribs, and to the transverse processes of all the dorsal 
vertebrae, and of the three posterior cervical. Action—to bend the back, 
and thus raise either the fore or hind quarter, when the other is fixed. 
It is the main agent in rearing and kicking, and is strongly called into 
play in galloping and leaping. 
SPINALIS DORSI is situated deeply on the sides of the withers. Origin 
—it is closely connected posteriorly with the last muscle, being attached 
to the spinous processes of the posterior dorsal vertebree. Jnsertion—to 
the spines of the six or seven anterior dorsal vertebrae, and the three or 
four posterior cervical. Action—to assist the longissimus dorsi in rearing 
and in raising the fore quarters in galloping. 
SEMI-SPINALIS DORSI is deeply buried beneath the two last muscles, 
with which it co-operates in its action. 
MUSCLES OF THE ABDOMEN. 
THESE ARE NATURALLY DIVIDED into two groups, according to the 
positions which they occupy and the offices they perform. Thus the 
superficial abdominal muscles form the lower walls of the cavity of the 
abdomen, while the deep abdominal muscles bound it anteriorly and 
superiorly. 
SUPERFICIAL ABDOMINAL REGION. 
THE ABDOMINAL MUSCLES, four in number, constitute the lower walls 
of the belly, and together form, as it were, a strong sheet, by means of 
which the intestines and abdominal organs are kept 'in position. After 
replecting the skin, they are seen to be covered by the panniculus car- 
nosus and a thick layer of yellow fibrous tissue, through which their 
division into tendon and muscle can faintly be discerned. These must be 
dissected off to bring into view the true abdominal muscles, when the 
following lines of demarcation will be discerned :— 
1. THE LINEA ALBA, which occupies the median line from the os pubis 
to the ensiform cartilage, and consists of a tough layer of white fibrous 
tissue, which unites the muscles of the abdomen together. At a little 
more than a third of its length from the pubes is found a lozenge-shaped 
space in which the tissue is almost entirely absent, and through which in 
the foetus the umbilical vessels pass. ‘his is the umbilicus, or navel, of 
the adult. 
2. On the surface of the rectus are several transverse white lines—the 
linez transversales, 
