THE SKULL. 163 



mitting of a very considerable range of movement as a whole, allows a sufficient degree of 

 mobility without any material diminution of strength. The many joints of which the spine is 

 composed, together with the very varied movements to which it is subjected, render it liable to 

 sprains ; but so closely are the individual vertebrae articulated that these sprains are rarely or 

 ever severe, and any amount of violence sufficiently great to produce tearing of the ligaments 

 would tend rather to cause a dislocation or fracture. The further safety of the column and its 

 less liability to injury is provided for by its disposition in curves, instead of in one straight line. 

 Fur it is an elastic column, and must first bend before it breaks : under these circumstances, 

 being made up of three curves, it represents three columns, and greater force is required to pro- 

 'lure bending of a short column than of a longer one that is equal to it in breadth and material. 

 Again, the safety of the column is provided for by the interposition of the intervertebral disk 

 bet ween the bodies of the vertebrae, which act as admirable buffers in counteracting the effects of 

 violent jars or shocks. Fracture-dislocation of the spine may be caused by direct or indirect 

 violence, or by a combination of the two, as when a person, falling from a height, strikes against 

 some prominence and is doubled over it. The fractures from indirect violence are the more com- 

 mon, and here the bodies of the vertebrae are compressed, whilst the arches are torn asunder ; 

 whilst in fractures from direct violence the arches are compressed and the bodies of the vertebrae 

 M-parated from each other. It will therefore be seen that in both classes of injury the spinal 

 marrow is the part least likely to be injured, and may escape damage even where there has been 

 considerable lesion of the bony framework. For. as Mr. Jacobson states, "being lodged in the 

 centre of the column, it occupies neutral ground in respect to forces which might cause fracture. 

 For it is a law in mechanics that when a beam, as of timber, is exposed to breakage and the 

 force does not exceed the limits of the strength of the material, one division resists compression, 

 another laceration of the particles, while the third, between the two. is in a negative condition." 1 

 Applying this principle to the spine, it will be seen that, whether the fracture-dislocation be pro- 

 duced by direct violence or indirect, one segment, either the anterior or posterior, will be exposed 

 to compression, the other to laceration, and the intermediate part, where the cord is situated, 

 will be in a neutral state. When a fracture-dislocation is produced by indirect violence the dis- 

 placement is almost always the same, the upper segment being driven forward on the lower, so 

 that the cord is compressed between the body of the vertebra below and the arch of the vertebra 

 above. 



The parts of the spine most liable to be injured are (1) the dorsi-lumbar region, for this part 

 is near the middle of the column, and there is therefore a greater amount of leverage, and more- 

 over the portion above is comparatively fixed, and the vertebrae which form it, though much 

 smaller, have nevertheless to bear almost as great a weight as those below ; (2) the cervico-dorsal 

 region, because here the flexible cervical portion of the spine joins the more fixed dorsal region ; 

 an 1 (3| the alto-axoid region, because it enjoys an extensive range of movement, and, being 

 near the skull, is influenced by violence applied to the head. In fracture-dislocation it has been 

 proposed to trephine the spine and remove portions of the laminae and spinous processes. The 

 operation can only be of use when the paralysis is due to the pressure of bone or the effusion of 

 blood, and not to cases, which are by far the most common, where the cord is crushed to a pulp. 

 And even in those cases where the cord is compressed by bone the portion of displaced bone 

 which presses on the cord is generally the body of the vertebra below, and is therefore inaccess- 

 ible to operation. The operative proceeding is one of great severity, involving an extensive and 

 deep wound and great risk of septic meningitis, and. as the advantages to be derived from it are 

 exceedingly problematical and confined to a very few cases, it is not often resorted to. Trephin- 

 ine has also been resorted to in some cases of paraplegia due to Pott s disease of the spine. 

 Here the paralysis is due to the pressure of inflammatory products, and where this is new scar- 

 tissue, formed by the organization of granulation tissue, its removal has been attended with a 

 very considerable amount of success. 



THE SKULL. 



The Skull, or superior expansion of the vertebral column, has been described 

 as if composed of four vertebrae, the elementary parts of which are specially 

 modified in form and size, and almost immovably connected, for the reception of 

 the brain and special organs of the senses. These vertebrae are the occipital, 

 parietal, frontal, and nasal. Descriptive anatomists, however, divide the skull 

 into two parts, the Cranium and the Face. The Cranium (x/>rfvoc, a helmet) is 

 composed of eight bones viz. the occipital, two parietal, frontal, two temporal, 

 KpJn'H'.>(<l. and ethmoid. The Face is composed of fourteen bones viz. the two 

 nasal, two superior maxillary, two lachrymal, two malar, two palate, two inferior 

 turbinated, corner, and inferior maxillary. The ossiculi audifrus, the teeth, and 

 Wonnian bones are not included in this enumeration. 



1 Holmes's System of Surgery, vol. i. p. 529, 1883. 



