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 venae cavae, beyond which it is almost 

 vertical. The right crus divides into two branches, which circumscribe the hiatus 

 cesophageus, 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 cm.) below the eighth thoracic vertebra, a little to the left of the median plane. 

 The foramen venae cavae 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. 



Muscles 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 coxae. 



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 Muscles 



The obliquus abdominis extemus is somewhat thinner and has a less extensive 

 origin, which begins at the lower part of the fifth intercostal 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 coxae, nor as high as the lumbar transverse proc- 

 esses. (In this region the abdominal tunic has a strong attachment to the point 



1 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 m 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. 



