69 



buffers in counteracting the effects of violent jars or shocks. Fracture dislocation of the vertebral 

 column 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 common, and here the bodies of the vertebrae are 

 compressed, while the arches are torn asunder; while in fractures from direct violence the arches 

 are compressed and the bodies of the vertebra? separated from each other. It will therefore be 

 seen that in both classes of injury the spinal cord is the part least likely to be injured, and mav 

 escape damage even when there has been considerable lesion of the bony framework. For, a*s 

 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 vertebral column, 

 it will be seen that, whether the fracture dislocation be produced by direct violence or by indirect 

 force, 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 displacement 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 vertebral column most liable to be injured are (1) the thoracolumbar region, 

 for this part is near the middle of the column, and there is therefore a greater amount of leverage, 

 and, moreover, 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- 

 thoracic region, because here the flexible cervical portion of the vertebral column joins the more 

 fixed thoracic region; and (3) the atlantoaxial 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, spinous processes and portions of the laminse may be removed (laminectomy} in order 

 to free the spinal cord from pressure, and to permit the surgeon to explore, to arrest hemorrhage, 

 to remove bone fragments, or to apply sutures. Laminectomy is also resorted to in some cases 

 of paraplegia due to Pott's disease of the spine. 



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 is composed of eight 

 bones, viz., the occipital, two parietals, frontal, two temporals, sphenoid, and ethmoid. 

 The Face is composed of fourteen bones, viz., the two nasals, two maxillce, two 

 lacrimals, two malars, two palates, two turbinates, vomer, and mandible. The ossic- 

 uli auditus, the teeth, and Wormian bones are not included in this enumeration. 



r Occipital. 

 Two parietals. 



n . , i Frontal. 



Cranium, 8 bones . < m i 



I wo temporals. 



I Sphenoid. 

 I Ethmoid. 



Skull, 22 bones 



Two nasals. 

 Two maxilla?. 

 Two lacrimals. 



i Two malars. 

 race, 14 bones . \ ^ 



Two palates. 



Two turbinates.' 



Vomer. 



Mandible^ 



The Hyoid Bone, situated at the root of the tongue and attached to the base 

 of the skull by ligaments, has also to be considered in this section. 



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



