100 OSTEOLOGY. 



slight traces of a transverse process and the rudiments of roots of the vertebral 

 arch. The succeeding segments are mere rounded or oval-shaped nodules of bone. 



Fusion between the lower elements occurs normally in middle life, whilst union between 

 the first and second segments occurs somewhat later. It is not unusual, however, to find 

 that the first coccygeal vertebra remains separate from the others. Though very variable, 

 as a rule, fusion occurs more commonly in the male, and at an earlier age, than in the 

 female. Szawlowski has recorded a case in which a curved process arose from the ventral 

 surface of the first coccygeal segment. He regards this as possibly the homologue of a 

 ventral arch (Anat. Anz. Jena, vol. xx. p. 320). 



From the posterior surface of the coccyx the glutaeus maximus arises, whilst 

 to it is attached the filum terminate of the spinal medulla. To its borders are 

 attached the coccygei and levatores ani muscles ; and from its tip spring the 

 fibres of the sphincter ani externus. 



THE VERTEBRAL COLUMN AS A WHOLE. 



When all the vertebrae are articulated together, the resulting column displays 

 certain characteristic features. The division of the column into a true or movable 

 part, comprising the members of the cervical, thoracic, and lumbar series, and 

 a false or fixed portion, including the sacrum and coccyx, can be readily 

 recognised. The vertebrae are so disposed that the bodies form an interrupted 

 column of solid parts anteriorly, which constitutes the axis of support for the 

 head and trunk; whilst the vertebral arches posteriorly provide a canal for the 

 lodgment and protection of the spinal medulla and its membranes. In the movable 

 part of the column both the anterior supporting axis and the vertebral canal are 

 liable to changes in their disposition, owing to the movements of the head and 

 trunk. Like the bodies and vertebral arches, the spinous and transverse processes 

 are also superposed, and fall in line, forming three series of interrupted ridges 

 one (the spinous) placed centrally and behind, the others (the transverse) placed 

 laterally. In this way two vertebral grooves are formed which lie between the 

 central and lateral ridges. The floor of each groove is formed by the laminae and 

 articular processes, and in these grooves are lodged many of the muscles which 

 serve to support and control the movements of the column. 



Further, the column so constituted is seen to display certain curves in an 

 antero- posterior direction. These curves are, of course, subject to very great 

 variation according to the position of the trunk and head, and can only be satis- 

 factorily studied in a fresh specimen ; but if care is exercised in the articulation 

 of the vertebras, the following characteristic features may be observed, assuming, of 

 course, that the column is erect and the head so placed that the axis of vision is 

 directed towards the horizon. There is a forward curve in the cervical region, 

 which gradually merges with the backward thoracic curve ; this becomes con- 

 tinuous below with an anterior convexity in the lumbar region, which ends more 

 or less abruptly at the union of the fifth lumbar with the first sacral vertebra, 

 where the sacrum slopes suddenly backwards, causing the column to form a 

 marked projection the sacro-vertebral angle. Below this, the anterior concavity of 

 the front of the sacrum is directed downwards as well as forwards. Of these four 

 curves, two the thoracic and sacral are primary, they alone exist during foetal 

 life ; whilst the cervical and lumbar forward curves only make their appearance 

 after birth the former being associated with the extension and elevation of the 

 head, whilst the latter is developed in connexion with the use of the hind limb in 

 the hyper-extended position, which in man is correlated with the assumption of 

 the erect posture ; this curve, therefore, only appears after the child has begun to 

 walk. For these reasons the cervical and lumbar curves are described as secondary 

 and compensatory. 



Not infrequently there is a slight lateral curvature in the thoracic region, the 

 convexity of the curve being usually directed towards the right side. This may 

 be associated with a greater use of the muscles of the right upper limb, or may 

 depend on the pressure exercised by the upper part of the thoracic aorta on the 



