THE BOXES OF THE TRUNK 



37 



The muscular attachments of the coccyx are as follows: the 

 gluteus maximus to the back of the upper three segments close to 

 the lateral border; the sphincter ani extemus to the tip; the 

 posterior fibres of the levator ani and a portion of the coccygeus 

 to the lateral border. The great and small sacro-sciatic ligaments 



Coccygeus 



Levator Ani 



dateas Maximus 



Comu 



Transverse Process 

 (mdimentar)-) 



_, Transverse Process 

 (rudimentary) 



Comu (rudimentary 



Sphincter Ani Extemus 



Fig. 27. — ^The Coccyx. 

 A, Anterior View; B, Posterior View. 



are partially attached to the lateral border of the first coccygeal 

 vertebra. 



The coccyx derives its blood-supply from the lower lateral 

 sacral and middle sacral arteries. 



Varieties. — The number of coccygeal segments may be increased to five, 

 due either to the addition of an extra nodule, or to incorporation of the fifth 

 sacral segment. The number may be reduced to three, due either to incorpora- 

 tion of the first coccygeal segment with the sacrum, or to suppression of one of 

 the nodules. 



Ossification. — The coccygeal vertebrae are cartilaginous at birth. Each 

 vertebra has one primary centre and two secondary centres, the first vertebra 

 having an additional pair of secondary centres. 



Primary Centres. — The primary- centre for the first vertebra appears from 

 the second to the fifth year; that for the second vertebra from the sixth to the 

 tenth year, and those for the third and fourth vertebrae about puberty. 



