40 LIGAMENTS AND MUSCLES OF THE HORSE. 



It is thickest at the prepubian tendon and along the median 

 line, and gradually thins out towards its circumference. 

 Anteriorly it extends a little underneath the posterior 

 deep pectoral muscle. 



Posteriorly in the male, it furnishes the suspensory ligaments of 

 the sheath, and in the female, analogous slips to the mam- 

 mary gland. 



It forms an elastic abdominal bandage, assisting tlie muscles, and 

 adapting the abdominal wall to the volume of its contents. 

 LiNEA Alba. 



This is a fibrous band extending from the ensiform cartilage to 

 the pubes, and is formed by the union of the aponeuroses 

 of the right and left muscles. 



1. External Oblique. 



Origi7i. — Outer surface of last fourteen ribs. 



Insertion. — To the linea alba, prepubian tendon, and the exter- 

 nal angle of the ilium. 



Action. — Together they arch the back. If the spine is fixed, 

 they draw the ribs back and assist in expiration. If both 

 spine and ribs are fixed, they assist in defaecation, urina- 

 tion, and parturition. Acting singly, the trunk is drawn 

 to the side of the muscle acting. 



2. Internal Oblique. 



Origin. — From the external angle of the ilium, and from the 



adjacent part of Poupart's ligament. 

 Insertion. — To the linea alba, prepubian tendon, and the last 



four (or five) costal cartilages. 

 Action.— '^iTuWa.v to ihe external ob-ique. 



3. Rectus Abdominis. 



Origin. — From the lower surface of the sternum, ctnd from the 



5th to the 9th costal cartilages, inclusive. 

 Insertion.— To the prepubian tendon. 

 Action. — It compresses the abdominal viscera and flexes the spine. 



It also draws the pelvis forward as in copulation. 



