336 THE ANATOMY OF THE HORSE. 



incline it laterally when a single muscle acts. If the pelvis be fixed it 

 will execute the same movements on the loins. 



Directions. — Raise the outer edge of the psoas magnus, and remove it 

 except its fibres of origin beneath the rim of the diaphragm and its 

 conical tendon of insertion, as in Plate 45. 



The Iliacus (Plates 16 and 45). This is a powerful fleshy muscle 

 which, when the psoas magnus muscle is in position, appears to consist 

 of an outer and an inner portion. In reality, however, it is a single 

 mass, with a deep groove in it for the terminal tendon of the psoas 

 magnus. It arises from the entire iliac surface of the ilium, from its 

 external angle, and from the sacro-iliac ligament. It is inserted into the 

 inner trochanter of the femur, in common with the psoas magnus. 



Action. — The same as the psoas magnus. 



The Quadratus Lumborum (Plate 45). This muscle lies under cover 

 of the great psoas muscle. Its most external and strongest fasciculus 

 arises from the sacro-iliac ligament. It is inserted by this same fasciculus 

 into the tips of the lumbar transverse processes, and into the hinder 

 edge of the last rib. From the main fasciculus others pass inwards to 

 the lumbar transverse processes, and to the under surfaces of the three 

 last ribs, close to the spine. 



Action. — To assist in bending the loins to the side of the acting 

 muscle. Both muscles, by fixing the last ribs, will enable the diaphragm 

 to act to more advantage. 



Lumbar Intertransverse Muscles (Plate 45). These are thin 

 muscular and tendinous strata connecting the edges of adjacent lumbar 

 transverse processes. 



Action. — To assist in bending the loins to the side on which the 

 muscle act. 



Directions — An examination of the diaphragm will complete the 

 dissection of the abdomen. Define its pillars attaching it to the lumbar 

 vertebrae, and clean the edges of its foramina. At its periphery, under 

 the costal cartilages, follow the asternal vessels (Plate 45). 



The Asternal Artery. This is one of the divisions of the internal 

 thoracic artery (Fig. 7, page 122). It passes from the thorax to the 

 abdomen by perforating the rim of the diaphragm about the 9th chondro- 

 costal joint. As here seen, it passes backwards at the rim of the 

 diaphragm, in the interval between it and the origin of the transversalis 

 abdominis, and terminates at the lower extremity of the 13th intercostal 

 space. It has three sets of branches, viz., (1) ascending branches, which 

 anastomose with the intercostal arteries of the spaces crossed ; (2) internal 

 branches to the diaphragm ; (3) descending branches, which run on the 

 peritoneal surface of the transversalis abdominis muscle. 



The Asternal Vein accompanies the artery. 



The Diaphragm (Plate 45) is the muscle which serves as a partition 



