54 THE SKELETON. 



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. 

 For 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- 

 duce 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 

 between 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 

 separated 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 arc (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 ; 

 and (3) the atlanto-axial 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- 

 ing 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 is supported on the summit of the vertebral column, and is of an 

 oval shape, wider behind than in front. It is composed of a series of flattened or 

 irregularly shaped bones which, with one exception (the lower jaw), are immovably 

 joined together. It is divided into two parts, the Cranium and the Face the 

 former of which constitutes a case for the accommodation and protection of the 

 brain, while opening on the face are the orifices of the nose and mouth ; between 

 the cranium above and the face below the orbital cavities are situated The 



/i / / ^ttyiwco ait; sjiuaieu. J. ne 



Cranium (xpdva< a helmet) is composed of eight bones-viz, the occipital two 

 panetal, frontal, two temporal, sphenoid, and ethmoid. The Face is composed 



tillary, two lachrymal, 



i v .-.._. ~.,.v W i-i/ w , wiiir.i j c*nd inferior maxillary. 



Ihe ossicuh auditus, the teeth, and Wormian bones are not included in this 

 enumeration. 



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



parietal, frontal,, two temporal, sphenoid, and ethmoid. The Face is composed 

 of fourteen bones viz., the two nasal, two superior maxillary, two lachrymal 

 two malar t^o palate, two inferior turbinated, vomer, and inferior maxillary. 

 ine ossicuti audit-fa, the froth onrl W~ * . ! i i , ? 



