64 THE ANATOMY OF THE HORSE. 



inner half of the anterior surface of the femur, meeting along the front 

 of the femur the vastus externus, and with it forming a groove in which 

 the rectis femoris rests. Its fibres are inserted into the inner ligament 

 of the patella, or into that bone along with the other divisions of the 

 quadriceps. 



Action. — It is an extensor of the stifle joint. 



Psoas Magnus and Iliacus (Plate 14). Only the terminal portion 

 of each of these muscles is here seen. They are more fully displayed 

 in the dissection of the sublumbar region, where the psoas magnus 

 arises from the last two ribs, and the vertebra? from the 16th dorsal 

 to the 5th lumbar (Plates 44 and 45). The iliacus arises from the 

 iliac surface and external angle of the ilium, and from the sacro-iliac 

 ligament. It presents a deep groove for the terminal portion of the 

 psoas magnus. The two muscles pass downwards beneath Poupart/g 

 ligament, and have a common insertion into the small (interna/) 

 trochanter of the femur. 



Action. — These muscles flex the hip-joint, and rotate it outwards. 



THE HIP AND OUTER ASPECT OF THE THIGH. 



Position. — The animal should be suspended in imitation of the 

 natural standing posture, by the means mentioned at page 8. 



Surface-marking. — A prominent feature of the region is the bony 

 projection formed by the external angle of the ilium (angle of the 

 haunch). The tuber ischii may also be felt by pressing deeply at 

 the point of the hip. At the highest part of the croup the internal 

 angle of the ilium (angle of the croup) may be felt, and in the middle 

 line the tips of the sacral spines are subcutaneous. In a lean 

 animal a number of grooves are seen marking the divisions of the 

 biceps and the line of opposition of that muscle with the semiten- 

 dinosus (Plate 15). 



Directions. — An incision through the skin is to be carried along the 

 middle line from the root of the tail as far forwards as the lumbar 

 region, where a transverse incision is to be carried outwards and down- 

 wards as far as the level of the angle of the haunch. Beginning at the 

 middle line above, the dissector is to reflect the skin from the limb, as 

 far as the middle of the leg. The first few inches of the skin will 

 require to be raised by the use of the scalpel, and then an attempt may 

 be made to tear it downwards off the limb — a method which will show 

 the cutaneous nerves distinctly without further dissection. 



Cutaneous Nerves. 1. Appearing a few inches from the middle 

 line are some slender branches derived from the sacral nerves. 2. Two 

 or three branches of considerable size, derived from the lumbar nerves, 

 pass backwards and downwards over the forepart of the gluteal region. 



