PRACTICAL CONSIDERATIONS : THE SPINE. 143 



PRACTICAL CONSIDERATIONS. 



While the number of vertebrae in the neck is almost invariable in man (and 

 indeed in all the mammalia except the sloth and the sea-cow), the length of the 

 cervical region varies greatly in individuals. As it is apparently shortened during 

 full inspiration and lengthened during full expiration, so an actual change in its 

 length is associated with the types of thorax that correspond to these conditions. 

 The long neck is therefore found in persons with chests that are flat above the 

 mammae, with wide upper intercostal spaces and narrow lower ones, and with lack of 

 prominence of the sternum. These conditions are often associated with phthisical 

 tendencies. The short neck is found in persons with chests of the reverse type. 

 Its theoretical association with apoplectic tendencies is very doubtful. 



The remaining variations both in the length and in the shape of the vertebral 

 column are closely connected with corresponding variations in its curves. 



The normal curves of the spine are four : the cervical, thoracic, lumbar, and 

 pelvic (or sacro-coccygeal). The cervical and lumbar are concave backward, the 

 thoracic and pelvic convex backward (Fig. 171). These curves are produced and 

 kept up partly by the twenty-three intervertebral disks. They are altered by disease. 

 An additional curve not uncommon in absolutely healthy persons consists in a slight 

 deflection of the thoracic spine to the right ; this asymmetry is usually ascribed to the 

 greater use of the right arm, but it is due to the position of the heart and the aorta. 



All the vertebral bodies are composed of cancellous tissue, which is more spongy 

 in direct proportion to the size of the vertebrae, and therefore is least so in the neck 

 and most spongy in the lumbar region. This corresponds with the greater succu- 

 lence and elasticity of the lower intervertebral disks and aids in minimizing the effect 

 of jars and shocks such as are received in alighting from a height upon the feet, the 

 lower portion of the column of course receiving the greater weight. If in such falls 

 the calcaneum or tibia is broken, the spine usually escapes injury. If the lower 

 extremity remains intact, the safety of the spine depends largely upon the elasticity 

 given by its curves and bv the disks. 



The fact that the bodies have to bear the chief strain of such shocks and of 

 extreme flexion and extension, the most usual forms of spinal injury, serves, together 

 with their comparative vascularity, to make them the seat of tuberculous infection 

 when it invades the spine. Their spongy texture, once they are softened by inflam- 

 mation, leads to their ready disintegration under the superincumbent weight. In 

 the neck and in the loins the process may at first merely cause a straightening of the 

 column, the normal curves being concave backward. In the thoracic region — the 

 most common situation — it soon produces kyphosis, an exaggerated backward curve, 

 the sharp projection of the spinous processes of the affected vertebrae causing it to 

 be known as ' ' angular curvature. ' ' The abscesses which result from caries of the 

 vertebrae are governed as to their position and course by the fasciae and muscles 

 that surround them. They will, therefore, be described later (page 643). 



The suspension of the whole body from the chin and occiput separates the indi- 

 vidual vertebrae so that they are- held together mainly by their ligaments. This 

 obviously relieves or removes the pressure of the superincumbent weight on the 

 bodies of diseased vertebrae. The relief of pressure in cases of thoracic caries is 

 continued by the use of appliances which transfer the weight of the head and 

 shoulders to the pelvis. The simplest of these is the plaster jacket. For cervical 

 caries, the weight of the head is transferred to the trunk beneath the level of disease 

 by means of an apparatus extending from above the head to a band (of leather or 

 plaster) encircling the chest. 



In cases of kyphosis corrected by the method of "forcible straightening" it 

 is obvious that a gap proportionate to the amount of bone which has previously 

 been destroyed must be left between the bodies of the diseased vertebrae. The 

 ultimate integrity of the spinal column will depend upon the extent and character 

 of the ankylosis which takes place between the separated vertebrae. It is asserted 

 (Calot) that such consolidation does occur between the bodies in moderately severe 

 cases, and between the laminae, transverse processes, and spines in the, more serious 



