ABDOMINAL MUSCLES 335 



ward, and is inserted into the outer part of the sternum and the 3rd and 

 4th sternal cartilages. 



Action. — It is not definitely known whether it contributes to inspiration 

 or expiration. 



ABDOMINAL MUSCLES 



Panniculus Carnosus. — This is a thin, broad sheet of muscular tissue 

 spread over a large extent of the surfece of the body, especially the sides 

 of the shoulder, chest, and belly, the front of the neck, and the sides of 

 the face. It is connected above and below with considerable aj^oneurotic 

 tendons, which attach it to the dorsal and lumbar spines, the fiank, the 

 inner side of the arm, the neck, and the abdominal tunic. 



Insertion. — By its fleshy fibres into the under surface of the integu- 

 ment. It is this muscle which imparts that vigorous movement to the 

 skin when flies or other matters irritate it and require to be dislodged. 



Abdominal Tunic. — When the panniculus carnosus is removed, a 

 broad sheet of yellow elastic tissue is exposed, spread over the under 

 surface and sides of the abdomen, to which the term " abdominal tunic " 

 is given. This elastic layer is tliick behind, and gradually thins as it 

 passes forwards and upwards over the sides of the belly. 



Posteriorly it divides and gives a layer to the sheath, which it supports 

 as in a sling. In the stallion this segment is of considerable thickness, 

 and assists in sustaining the penis when in a state of erection. It is known 

 as the " suspensory ligament of the sheath ". 



In the female a similar division takes place, by which each milk-gland 

 becomes invested in an elastic capsule. Generally considered, the abdo- 

 minal tunic supplies a large bandage, which braces up the abdominal 

 muscles and enables them to support the weight of the organs con- 

 tained in the belly. In old brood mares it is of considerable thickness, 

 owing to the additional weight imposed upon the walls of the belly during 

 a succession of pregnancies. 



The muscles proper to the abdomen are eight in number, four on either 

 side. They comprise the external oblique muscles, the internal oblique, 

 the transversalis, and the straight. 



The three first named possess broad, aponeurotic tendons, all of which 

 converge towards the centre of the belly and intermix their fibres, as a 

 result of which a dense white band is formed, extending from the pubis 

 behind to the sternum in front. This band is termed " linea alba " or 

 Avliite line. A little behind the middle of this line a lozenge-shaped space 

 appears, in which the umbilical opening or navel originally existed. 



