THE SPINE IN GENERAL. 



51 



of the coccyx are narrow, and give attach- 



J 3 . . , . 1st cervical 



ment on each side to the sacro-sciatic liga- or Atlas. 



merits, to the Coccygeus muscles in front of 

 IT ,i /^ii , 2nd cervical 



the ligaments, and to the Gluteus inaximus 



behind them. The base presents an oval sur- 

 face for articulation with the sacrum. The 

 apex is rounded, and has attached to it the 

 tendon of the external Sphincter muscle. It 

 is occasionally bifid, and sometimes deflected 

 to one or other side. 



Development. The coccyx is developed 

 by four centres, one for each piece. Occa- 

 sionally one of the first three pieces of this 

 bone is developed by two centres, placed side 

 by side. The ossific nuclei make their ap- 

 pearance in the following order : in the first 

 segment, shortly after birth ; in the second 

 piece, at from five to ten years ; in the third, 

 from ten to fifteen years ; in the fourth, from 

 fifteen to twenty years. As age advances 

 these various segments become united Avith 

 each other from below upward, the union 

 between the first and second segments being 

 frequently delayed until after the age of 

 twenty-five or thirty. At a late period of 

 life, especially in females, the coccyx often 

 becomes joined to the end of the sacrum. 



Articulation. With the sacrum. 



Attachment of Muscles. To four pairs 

 and one single muscle : on either side, the 

 Coccygeus ; behind, the Gluteus maximus 

 and Extensor coccygis, when present ; at the 

 apex, the Sphincter ani ; and in front, the 

 Levator ani. 



6-\ 



7-1 



1st dorsal.^ 



""Si 



The Spine in General. 



The Spinal Column, formed by the junc- 

 tion of the vertebrae, is situated in the median 

 line, at the posterior part of the trunk ; its 

 average length is about two feet two or three 

 inches, measuring along the curved anterior 

 surface of the column. Of this length the 

 cervical part measures about five, the dorsal 

 about eleven, the lumbar about seven inches, 

 and the sacrum and coccyx the remainder. 

 The female spine is about one inch less than 

 that of the male. 



Viewed in front, it presents two pyramids 

 joined together at their bases, the upper one 

 being formed by all the vertebrae from the 

 second cervical to the last lumbar, the lower 

 one by the sacrum and coccyx. When ex- 

 amined more closely, the upper pyramid is 

 seen to be formed of three smaller pyramids. 

 The uppermost of these consists of the six 



1st lumbar.- 



5- 



Sacrum. 



Coccyx. 

 FIG. 22. Lateral view of the spine. 



