MUSCLES OF THE TRUNK. 



273 



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

 muscles are distinguished as sacro-coccygeus superior, sacro-coccygeus 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 the supra-sacral spine, or from the coccygeal vertebrse 

 themselves. The tendons for their movable insertion into these vertebrae are 

 always very short. 



This muscle, covered by the coccygeal aponeurosis, in turn covers the vertebrae 

 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 semispinahs 

 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 precedmg ; its constituent fasciculi take their origin from the 



Fi?. 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, crureus. 



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 vertebrae. 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 

 {compressor 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 



