160 



THE SKELETON. 



FIG. 129. Lateral view of the spine. 



series of small eminences, which represent 

 the transverse processes of the coccygeal 

 vertebrae. Of these, the first on each side is 

 the largest, flattened from before backward, 

 and often ascends to join the lower part of 

 the thin lateral edge of the sacrum, thus 

 completing the fifth anterior sacral foramen 

 for the transmission of the anterior division 

 of the fifth sacral nerve ; the others diminish 

 in size from above downward, and are often 

 wanting. The borders of the coccyx are 

 narrow, and give attachment on each side to 

 the sacro-sciatic ligaments, to the Coccygeus 

 muscle in front of the ligaments, and to the 

 Gluteus maximus behind them. The base 

 presents an oval surface 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, at birth ; in the second piece, at 

 from five to ten years; in the third, from 

 ten to fifteen years ; in the fourth, from fif- 

 teen to twenty years. As age advances these 

 various segments become united in the fol- 

 lowing order: the first two pieces join; then 

 the third and fourth ; and, lastly, the bone 

 is completed by the union of the second and 

 third. 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. 



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 

 the male. 



