MUSCLES OF THE TRUNK. 



273 



inserted into each of the coccygeal bones. With regard to their situation, these 

 miLScles are distinguished as sacro-coccygeus superior, sacro-coccijgeus inferior, and 

 sacro-coccygeus lateralis. 



A. Sacro-coccygeus Superior (Erector Coccygis). — The fasciculi which 

 form this muscle have their fixed insertion either in the summits and sides of the 

 three or four last processes of tlie supra-sacral spine, or from the coccygeal vertebrae 

 tliemselves. The tendons for their movable insertion into these vertebraB are 

 always very short. 



This muscle, co\ered by the coccygeal aponeurosis, in turn covera the vertebras 

 it moves. It responds : inwardly, to the analogous muscle of the opposite side ; 

 outwardly, to the lateral sacro-coccygeus, and, near its anterior extremity, to a 

 very strong aponeurotic expansion which separates it from the semispinalis 

 muscle. It directly elevates the tail, or pulls it to one side, according as it acts 

 in concert with its fellow or singly. 



B. Sacro-coccygeus Inferior (Depressor Coccygis). — This muscle is 

 thicker than the preceding ; its constituent fasciculi take theii- origin from the 



Ficr. 167. 



SACRO-ILIAC AND COXO-FEMORAL ARTICULATIONS, WITH THEIR SURROUNDING MUSCLES. 



1, Sacro-coccygeus superior; 2, sacro-coccygeus lateralis; 3, sacro-coccygeus inferior,* 4, ischio« 

 coccygeus ; 5, deep gluteus; 6, criireus. 



inferior surface of the sacrum, towards the third vertebra, and from the internal 

 face of the sacro-sciatic ligament and the coccygeal bones. It readily divides into 

 two parallel portions, which Bourgelat has described as two separate muscles. 

 The fasciculi of the internal portion are inserted, by their posterior extremity, into 

 the inferior face of the first coccygeal vertebras. Those of the external portion 

 are furnished with strong superficial tendons, nearly all of which are for the 

 bones of the tail. 



This muscle responds : outwardly, to the sciatic ligament, the ischio-coccygeus 

 {ronpressor coccygeus) and coccygeal aponeurosis ; inwardly, to the muscle of the 

 opposite side, and to the coccygeal attachment of the rectum ; above, to the 

 sacrum, the bones of the tail, and the lateral muscle ; below, to the rectum and 

 the coccygeal aponeurosis. 



It either directly depresses the tail or inclines it to one side. 



C. Sacro-coccygeus Lateralis (Curvator Coccygis). — This muscle may 



