THE SPINE IN GENERAL. 



131 



Fig. 87. Coccyx. 

 Cornua 



points of junction of the different pieces. It has attached to it the anterior 

 sacro-coccygeal ligament and Levator Ani muscle, and supports the lower end 

 of the rectum. The posterior surface is convex, 

 marked by transverse grooves similar to those on 

 the anterior surface; and presents on each side a 

 lineal row of tubercles, the rudimentary articular 

 processes of the coccygeal vertebrae. Of these, the 

 superior pair are very large; and are called the 

 cornua of the coccyx; they project upwards, and 

 articulate with the cornua of the sacrum, the junc- 

 tion between these two bones completing the fifth 

 sacral foramen for the transmission of the posterior 

 branch of the fifth sacral nerve. The lateral borders 

 are thin, and present a series of small eminences, 

 which represent the transverse processes of the coccy- 

 geal vertebrae. Of these, the first on each side is of 

 large size, flattened from before backwards ; and often 

 ascends to join the lower part of the thin lateral 

 edge of the sacrum, thus completing the fifth sacral 

 foramen: the others diminish in size from above 

 downwards, and are often wanting. The borders of 

 the coccyx are narrow, and give attachment on each 

 side to the sacro-sciatic ligaments and Coccygeus 

 muscle. The base presents an oval surface for articu- 

 lation with the sacrum. The apex is rounded, and 

 has attached to it the tendon of the External Sphinc- 

 ter 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. Occasionally, one of the 

 first three pieces of this bone is developed by two 

 centres, placed side by side. The ossific nuclei make their appearance 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 

 fifteen to twenty years. As age advances, these various segments become 

 united in the following 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 later period of life, especially in females, the coccyx often becomes joined 

 to the end of the sacrum. 



Articulation. With the sacrum. 



Attachment of Muscles. On either side, the Coccygeus ; behind, the Gluteus 

 Maximus; at the apex, the Sphincter Ani; and in front, the Levator Ani. 



OF THE SPINE IN GENERAL. 



The Spinal Column, formed by the junction 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, measured 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 remain- 

 der. 



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 examined more 

 closely, the upper pyramid is seen to be formed of three smaller pyramids. 

 The uppermost of these consists of the six lower cervical vertebrae ; its apex 

 being formed by the axis or second cervical ; its base, by the first dorsal. The 



Posterior iSit.-rfa.ca 



