TOPOGRAPHIC 



AND 



APPLIED ANATOMY. 



THE HEAD. 



The study of the practical anatomy of the head has for its essential foundation a knowledge 

 of the bones of the skull (Fig. i). The cranium, surrounding the brain like a capsule, is dis- 

 tinguished from the face, which holds relation to the beginnings of the intestinal and respiratory 

 tracts and to important sense-organs, particularly to the organ of vision. The external boun- 

 daries between the cranium and the face are formed by the superior margin of the orbit, the 

 zygoma, and the external auditory meatus. In conformity with these divisions of the skull, the 

 head is subdivided into a cranial region and a facial region. 



THE CRANIAL REGION. 

 THE CRANIUM. 



The cranium is formed by the following bones : 



(a) Four single bones: (i) The occipital, (2) the sphenoid, (3) the ethmoid, (4) the frontal. 



(b) Two paired bones: (i) The parietal, (2) the temporal. 



Portions of some of these bones are also found in the facial group, the greater portion of the 

 ethmoid, for example. The relations of these bones become clearer if we remember that the 

 broad sagittal ring formed by the single bones is open above and is converted into a closed chamber 

 by the broad frontal ring of the paired bones, which is open below. The superior or arched 

 portion of the cranium is known as the vertex or vault, while the inferior or flatter portion is 

 called the base of the skull. The plane of the base of the skull dips posteriorly and forms the 

 chord, so to speak, of the large arc of the cranial vault. 



The thickness of the cranium is of great importance, particularly with reference to the prog- 

 nosis of injuries. It varies with age, with the individual, and above all with location. Between 

 the extremes of the so-called paper-skulls, scarcely two millimeters thick, and those skulls which 

 are called hypertrophic, measuring one centimeter or even more in thickness, there are many in- 

 termediate degrees. The average thickness of the cranial vault is five millimeters. Disregard- 

 ing the thin portions of the base (see page 22), a knowledge of which is particularly important for 

 the understanding of fractures in this situation, local thinnings of the skull are produced: 



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