42 THE HORSE IN MOTION. 



If the reader will refer to Plate III. he will see only a portion of 

 this muscle ; its extent forward is concealed by the pearly-colored apo- 

 neurosis which completely covered it and is only partially dissected 

 away; and by comparison with Plate VIII. and the skeleton, Plate II., 

 he will find little difficulty in understanding the relations of this muscle 

 with the surrounding parts. In the 'succeeding Plate IV. the whole 

 outer face of it is exposed except the extreme posterior border, which 

 is covered by the long vastus muscle crossing its fibres diagonally; the 

 concavity in the ridge of the ilium from b to g, Plate VIII., shows also 

 the aponeurosis which covers the ilio spinalis and which serves as 

 a base for the attachment of the gluteus forward of the ilium. At 

 Plate V., h, are seen the attachments by tendon of the great gluteus to 

 the trochanter. (See skeleton, Plate II.) The centre of motion, or 

 head of the femur, for the posterior limb is a little in front of this, lies 

 deeper, and cannot be felt externally. This trochanter, therefore, is 

 relied upon by horsemen as a point for measurement, and is known to 

 them as the " whirlbone." Referring again to Plate VIII., the severed 

 tendons of the great gluteus may be seen at c, c. 



The deep gluteus is well shown at P, Plate VIII. It arises on 

 the shaft of the ilium, and its fibres follow the course of that bone and 

 adhere to it as they descend. Its muscular fibres are intermingled 

 with tendinous bands following the same course, and the insertion of 

 the muscle is into the neck of the femur, or thigh bone, just outside 

 of the capsular ligament. Its curious construction of mingled bands 

 of tendon and muscle gives it the properties of both, the passive re- 

 sistance of the former and the active aggressive force of muscular fibre. 

 The spiral course of its fibres indicates that it is intended to rotate the 

 leg outward, but more especially to hold the head of the femur in its 

 socket. Its influence in locomotion must be small. 



The long vastus is second only to the great gluteus in weight, 

 its equal in length, and from its great advantage of position much 

 superior to it in effective power to perform the work required of 

 it. Its position may be seen in v, Plates III., IV., IX., and in Plate 

 V. its absence is more conspicuous than its presence could be. Its 

 insertion is into the external condyle of the femur (see Plates II. 



