MUSCULAR SYSTEM. 131 



which part it is also more closely adherent to the muscle, in con- 

 sequence of the cellular substance there is interposed. 



These muscles are divisible into four pairs ; and most com- 

 pletely so at their origins at the root of the tail : in the course of 

 their progress their nearest fibres unite together, and become 

 blended one with another. 



ERECTOR coccYGis. — Saci'o-coccj/geus superior. 



Situaiion. — Supero-lateral part of the tail. 



Form. — Elongated ; pyramidal. 



Attachment. — Anteriorly and superiorly, to the transverse pro- 

 cesses and spines of the sacrum ; posteriorly and inferioily, to the 

 bodies and spines of the bones of the coccyx. 



Relations. — The muscle lies in the hollow formed by the 

 sacrum on the inner side, and the ileum and sacro-sciatic liga- 

 ment on the outer side. 



Structure. — Superior attachments, tendinous and fleshy ; infe- 

 rior, chiefly fleshy ; though, here and there, slips of tendon pierce 

 its belly and take root in the bone. The muscle, altogether, is 

 remarkable for its tendinous appearance externally, and for being 

 somewhat complex in its composition: consisting, exteriorly, of 

 a flat tendon, from which slips are detached in its course along 

 the tail, after a penniform manner, across its fleshy belly j 

 while the interior partis fleshy, and grows pale and narrow in its 

 course, and is everywhere closely adherent to the coccygeal 

 bones. Towards the extremity of the dock, the tendons so pre- 

 dominate over the fleshy fibres, that it is through them alone 

 that the muscle can be distinctly traced to its termination. 



Action. — To erect the tail. If one muscle act by itself, the 

 tail at the time of elevation will be carried to one side. Some 

 horses have such power of action with these muscles, that they 

 can reflex the tail over the croup, or curve it to either side, 

 around the quarter. 



DEPRESSOR COCCYGIS. — Sacro-cocci/geus inferior. 



Situation. — Infero-lateral part of the tail. 



JPorw. — Similar to that of the preceding muscle. 



Attachment. — Anteriorly and superiorly, within the pelvis, to 

 the sacro-sciatic ligament, and to the body of the sacrum ; pos- 

 teriorly and inferiorly, to the inferior parts of the bodies of the 

 coccygeal bones. 



Relations. — Superiorly, with the erector; inferiorly and exter- 

 nally, with the skin ; internally, with the coccyx. 



Structure. — Like the preceding muscle, it has, exteriorly, a 

 flattened tendon : but it is a much smaller one, and docs not 



