66 THE HORSE IN MOTION. 



considerable mass, and join on to the serratus, s, so nearly in the 

 line of the centre of motion that it may be that they act in con- 

 junction with the trachelo subscapularis, whose insertion is at g, 

 Plate XI. 



The last-named muscle is well exposed in Plate IV., g, g. As 

 there seen, it is triangular. It arises from the transverse processes of 

 the last six cervical vertebra, and its fibres converge to their inser- 

 tion on the inner face of the scapula, in front of the insertion of the 

 serratus, or centre of motion. Its muscular fibres are in little fasci- 

 culce, or bundles, separated by interstitial fibrous or cellular tissue, 

 to admit of great freedom of motion upon each other in the extreme 

 vertical flexions of the neck while grazing. It is a powerful muscle, 

 its weight being three and a half pounds ; but its action has not been 

 comprehended, its fibres being nearly horizontal on an average, or a 

 little upward, and their insertion on a line with the centre of motion ; 

 it can have no active agency in locomotion, though with the joint 

 action of the levator anguli scapulae it may move the upper end of the 

 scapula forward, as far as permitted by the tendinous fibres of the 

 serratus and the branch from the yellow cord ; but that cannot be 

 much. Until the theory of quadrupedal motion was understood its 

 function may well have been overlooked. It is now clear. Its attach- 

 ment being on a line with the centre of motion and directly upon a 

 fixed point, it cannot be supposed to aid in the motion of the scapula 

 about that point; but when the animal is running, and the fore leg 

 is thrown forward and takes the ground, it is required alone to 

 receive the weight of the whole body or be itself crushed by its 

 momentum. This will be resumed after the action of the triceps 

 brachii at the same instant is shown. It is sufficient for the present 

 that the action of this muscle abstractly be understood and remem- 

 bered. Its general appearance is so like the muscle above it, the 

 scale nus (m, m, m), having similar origins along the cervical ver- 

 tebra nearer the head, and its insertions into the spines of the dorsal 

 vertebra (hidden in the plate by the overlaying levator anguli scap- 

 ulae), that it is apt to be confounded with it; but the scalenus is 

 not a locomotive muscle, its function being to raise the head when 



