MUSCLES OF THE THORAX—ABDOMINAL MUSCLES 349 
MUSCLES OF THE THORAX 
The levatores costarum number ten or eleven pairs. 
The external intercostal muscles are thick; they terminate at the costo- 
chondral junctions. The internal intercostals are specially thick in relation to the 
cartilages of the sternal ribs; here there exist bundles (comparable to the levatores 
costarum) which are attached in front to the sternum, behind to a costal cartilage. 
The interosseous part thins toward the upper end of the spaces. 
The diaphragm presents several important differential features. Its slope is 
much steeper and its width is greater than in the horse. The upper limit of the 
costal attachment extends almost in a straight line from the last rib about a hand- 
breadth above its middle to the junction of the eighth rib with its cartilage, and 
along the latter to the sternum. The midline slopes from the twelfth thoracic 
vertebra obliquely as far as the foramen ven cave, beyond which it is almost 
vertical. The right crus divides into two branches, which circumscribe the hiatus 
csophageus, unite below, and then spread out in the tendinous center. The left 
crus is small. The hiatus cesophageus is situated about four to five inches (10 to 
12 em.) below the eighth thoracic vertebra, a little to the left of the median plane. 
The foramen ven cave is a little more ventral and almost in the median plane.* 
In the sheep the costal attachment differs from that of the ox. The upper 
limit of the attachment extends in a gentle curve (convex ventrally) from the 
last rib about the junction of its middle and ventral thirds to the ventral end of 
the ninth rib. 
JIUSCLES OF THE BACK AND LOINS 
The serratus dorsalis anterior is very thin. It is inserted on the fifth to the 
eighth ribs when fully developed, but it may be reduced to two or three digitations 
or may be absent. The serratus dorsalis posterior is inserted on the last three or 
four ribs. 
The longissimus costarum has a distinct lumbar portion which is attached to 
the lumbar transverse processes and the tuber cox. 
The longissimus dorsi resembles that of the horse, but it is more fleshy anter- 
iorly, and the spinalis dorsi is clearly distinguishable from the common mass. In 
the lumbar region the tendons meet across the summits of the spines. 
Intertransversales are present in the back, and interspinales in the back and 
loins. ° 
MUSCLES OF THE TAIL 
These resemble in general those of the horse; the coccygeus is, however, much 
more developed. 
ABDOMINAL MMUSCLES 
The obliquus abdominis externus is somewhat thinner and has a less extensive 
origi, which begins at the lower part of the fifth mtercostal space and ends on 
the last rib above its middle. The direction of the fibers in the flank is horizontal, 
and they do not reach to the tuber cox, nor as high as the lumbar transverse proc- 
esses. (In this region the abdominal tunic has a strong attachment to the point 
__ ‘The sternal part is clearly separable from the costal part. The costal attachment is much 
higher posteriorly than in the horse, thus diminishing the capacity of the thorax in comparison 
with that animal. The last digitation is thus some seven or eight inches (ca. 18 to 20 cm.) above the 
corresponding digitation of the transversus abdominis. There are small intermediate digitations 
at the last two intercostal spaces. 
