DISSECTION OF THE POSTERIOR LIMB. 63 



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 vertebrae from the 16th dorsal to the 5th 

 lumbar (Plates 44 and 45). The iliacus m-ises 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's ligament, and have a com- 

 mon insertion into the small (internal) trochanter of the femur. 



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



THE HIP AND OUTER ASPECT OP 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 pro- 

 jection 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 semitendinosus (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 haimch. 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. 



3. A few inches below the point of the hip a cutaneous branch derived 

 from one of the posterior gluteal nei-ves appears from between the biceps 

 and semitendinosus, and separates into a number of radiating filaments. 



4. On a level with the stifle-joint the p<^roneal-cutaneous branch of the 

 external popliteal nerve comes out through the biceps, and is distributed 

 on the outer side of the leg. 



