20 COCCYX. 



Development. By twenty-one points of ossification ; five for each of 

 the three first pieces, viz. one for the "body, one for each lateral por- 

 tion, and one for each lamina ; and three for each of the two last, 

 namely, one for the body, and one for each lateral portion. In the 

 progress of growth, and after puberty, fourteen epiphysal centres are 

 added, namely, two for the surfaces of each body, one for each auricu- 

 lar surface, and one for the thin edge of each lateral border. Ossifica- 

 tion begins in the bodies of the sacral pieces somewhat later than in 

 those of the true vertebrae ; the first three appearing during the eighth 

 and ninth week, and the last two at about the middle of intra-uterine 

 existence. Ossification of the lamella? takes place during the interval 

 between the sixth and the ninth month. The epiphyses for the upper 

 and under surface of the bodies are developed during the interval be- 

 tween the fifteenth and eighteenth year ; and for the auricular and 

 marginal piece, after twenty. The two lower vertebral pieces, although 

 the last to appear, are the first to be completed (between the fourth and 

 fifth year), and to unite by their bodies. The union of the bodies 

 takes place from below upwards, and finishes between the twenty- 

 fifth and the thirtieth year, with the first two pieces. 



Articulations. With four bones; the last lumbar vertebra, ossa 

 innominata, and coccyx. 



Attachment of Muscles. To seven pairs ; in front the pyriformis, 

 on the side the coccygeus, and behind the gluteus maximus, latissimus 

 dorsi, longissimus dor si, sacro-lumbalis, and multifidus spinae. 



The COCCYX (X,'OKKV\ cuckoo, from resembling a cuckoo's beak) is 

 composed of four small pieces, which form the caudal termination of 

 the vertebral column. The superior piece is broad, and expands late- 

 rally into two transverse processes ; it is surmounted by an oval arti- 

 cular surface and two cornua, the former to articulate with the apex of 

 the sacrum, and the latter with the sacral cornua. The lateral wings 

 sometimes become connected with the sacrum, and convert the notches 

 for the fifth pair of sacral nerves into foramina. The remaining three 

 pieces diminish in size from above downwards. 



Development. By four centres, one for each piece. Ossification 

 commences in the first piece soon after birth ; in the second, between 

 five and ten years ; in the third, between ten and fifteen ; and in 

 the fourth between fifteen and twenty. The pieces unite at an earlier 

 period than the bodies of the sacrum, the two first pieces first, then 

 the third and fourth, and lastly the second and third. Between forty 

 and sixty years, the coccyx becomes consolidated with the sacrum ; 

 this event taking place later in the female than in the male. 



Articulations. With the sacrum. 



Attachment of Muscles. To three pairs, and one single muscle : 

 gluteus maximus, coccygeus, posterior fibres of the levator ani, and 

 sphincter ani. 



