THE VERTEBRAL COLUMN AS A WHOLE 43 



into three parts is indicated by transverse grooves. In advanced life the pieces 

 of the coccyx, having previously united to form one bone, may also become 

 joined to the sacrum. 



The first piece of the coccyx is much broader than the others. It consists of a body, 

 transverse processes, and rudiments of a neural arch. The body presents on its upper surface 

 an oval facet for articulation with the apex of the sacrum. On each side of the body a trans- 

 verse process projects laterally and is joined either by ligament or bone to the inferior lateral 

 angle of the sacrum, forming a foramen for the anterior division of the fifth sacral nerve. From 

 the posterior surface of the body two long coccygeal cornua project upward and are connected to 

 the sacral cornua by the posterior sacro-coccygeal ligaments, enclosing on each side an aperture 

 — -the last intervertebral foramen — for the exit of the fifth sacral nerve. The coccygeal cornua 

 represent the roots and superior articular processes of the first coccygeal vertebra. 



The second piece of the coccyx is much smaller than the first, and consists of a body, 

 traces of transverse processes, and a neural arch, in the form of slight tubercles at the sides and 

 on the posterior aspect of the body. 



The third and fourth pieces of the coccyx, smaller than the second piece, are mere nodules 

 of bone, corresponding solely to vertebral bodies. 



The anterior surface of the coccyx gives attachment to the anterior sacro-coccygeal ligament 

 and near the tip to the levator ani; it is in relation with the posterior surface of the rectum. 



The posterior surface of the coccyx is convex, and the upper three pieces afford attachment 

 to the gluteus maximus on each side, and the last piece to the coccygeal portion of the sphincter 

 ani externus. 



The lateral margins are thin, and receive parts of the sacro-sciatic ligaments, of the 

 coccygei muscles, and of the levatores ani. 



THE VERTEBRAL COLUMN AS A WHOLE 



The vertebral column (fig. 48) is the central axis of the skeleton and is situated in the 

 median line at the posterior aspect of the trunk. Superiorly it supports the skull; laterally it 

 gives attachment to the ribs, through which it receives the weight of the upper hmbs, and 

 inferiorly it is supported by the hip bones, by which the weight of the trunk is transmitted to 

 the lower limbs. Its length varies in different skeletons, but on an average it measures about 

 70 cm. (28 in.) in the male and about 2.5 cm. (1 in.) less in the female. To the entire length the 

 cervical region contributes 12.5 cm. (5 in.), the thoracic 27.5 cm. (11 in.), the lumbar 17.5 cm. 

 (7 in.), and the sacro-coccygeal portion the remaining 12.5 cm. (5 in.). The vertebral column 

 presents a series of curvatures, four when viewed in profile and one when viewed from the front 

 or back. The former are directed alternately forward and backward, and are named, from the 

 regions of the column in which they occur, cervical, thoracic, lumbar, and sacral. The fifth 

 curve is lateral, being in most cases directed toward the right side. 



The cervical, thoracic and lumbar curvatures pass imperceptibly into one another, but at 

 the junction of the last lumbar vertebra with the sacrum a well-marked angle occurs, known as 

 the sacro -vertebral or lumbo-sacral angle, with the result that the promontory of the sacrum 

 overhangs the cavity of the minor (small) pelvis and forms a portion of the superior aperture of 

 the small pelvis. 



The thoracic and sacral curves have their concavities directed forward and are developed 

 during intra-uterine life. They are in obvious relation to two great cavities of the trunk, 

 thoracic and pelvic, and may be regarded as primary or accommodation Cil£ZSS> for the thoracic 

 and pelvic viscera. The thoracic curve extends from the second to the twelfth thoracic vertebra 

 and the sacral curve coincides with the sacrum and coccyx. , 



The cervical and lumbar curves have their convexities directed forward, and are developed \ 

 during the first year after birth. They are essentially curves of compensation, necessary for \ 

 the maintenance of the upright posture, and are brought about by modifications in the shape 

 of the intervertebral discs. The cervical curve is formed about the third month, or as soon as 

 the infant can sit upright. The great pecuharity of the curve is that it is never consohdated. 

 being present when the body is placed in the erect position and obliterated by bending the head 

 down upon the chest. The lumbar curve is developed about the end of the first year or when the 

 child begins to walk, but is not consohdated until adult life. (Symington.) The cervical curve 

 extends from the atlas to the second thoracic vertebra, and the lumbar curve from the twelfth 

 thoracic to the promontory of the sacrum. . • u • 



The lateral curve is situated in the upper thoracic region, and when directed to the right is 

 probablv associated with the greater use made of the right hand. This curve, however, is 

 particularly liable to modification in different occupations and in different races. 



Viewed from the front, the vertebral column presents a series of pyramids due to the 

 successive increase and decrease in size of the bodies. These become broader from the axis to 

 the first thoracic vertebra and then decrease to the fourth thoracic. The first pyramid therefore 

 includes all the cervical vertebrae except the atlas, and has the apex directed upward and its 

 base downward, whilst the second is inverted and formed by the first four thoracic vertebrae. 

 The third pyramid, much the longest, is the result of the increase in size from the fourth thoracic 

 to the fifth lumbar vertebra, and the fourth, which is inverted, is produced by the rapid contrac- 

 tion of the sacral and coccygeal vertebrae. j u * 



Viewed from behind, the spinous processes project in the middle fine, and the transverse 

 processes as two lateral rows. Of the spines, those of the axis, seventh cervical, first thoracic, 

 and the lumbar vertebra} appear most prominent. On each side is the vertebral groove, the 

 floor of which is formed in the cervical and lumbar regions by the laminae and articular processes. 



( 



