THE HORSE IN MOTION. 43 



and V.), and its relations are so perfectly shown in the plates as to 

 scarcely require description. Plate IV. shows the superficial gluteus 

 removed and the anterior margin of the long vastus exposed. It 

 has its origin on spines of the sacrum posterior to those occupied 

 by the superficial gluteus ; it fills the deep fossa anterior to the 

 tuberosity of the ischium, and overlaps the hip joint four inches ; 

 being lodged in this deep fossa, its position is fixed at that point; 

 its direction is then changed so as to run downward and forward 

 until it reaches the lower end of the femur, where its tendon is con- 

 founded with that of the patella. 



.\s thus described, the posterior branch, which is admitted by 

 anatomists to be distinct in structure and function, is detached. (It 

 is marked s' in Plate V.) This is done for reasons which will be 

 given when we come to consider the semi-tendinosus. Its weight,, as 

 so limited, is nine pounds, its length twenty-six inches. The space 

 occupied on the surface in front of the tuberosity of the ischium 

 is eight inches, or four inches over the trochanter of the femur, and 

 the circumference of the body of the muscle at that point is fifteen 

 inches. 



It is nearly uniform in thickness throughout, except as its mus- 

 cular fibres give way to tendinous ones toward its lower insertion. 

 While the great gluteus has some of its fibres measuring as long, the 

 great mass of them, on which its strength depends, are not half that 

 length. The concentration of the fibres of the gluteus before their 

 insertion into the trochanter is very great, and as their power depends 

 upon their number and not upon their length, that of this muscle is 

 enormous. Though it acts on the short end of the lever, the line of 

 its action is very direct. But the vastus acts upon the extremity 

 of the long end of the lever, and from the great length of its fibres 

 sustains its action for a long time. These muscles hold a very 

 interesting relation ; they supplement one another. The power of 

 the gluteus is effective in giving velocity, as in kicking; that of 

 the vastus is effective in pushing the body over the foot on the 

 corresponding side, when it is fixed upon the ground, as in rearing 

 and leaping ; in the hare, whose mode of progression is by a sue- 



