158 SKELETON. 



the emissaries of Santorini. Moreover, there are communica- , 

 tions sent from the diploic veins, through the porosities of the 

 internal table of the skull, to the veins of the dura mater. This 

 fact is rendered very evident by tearing off the skull-cap, when 

 the surface of the dura mater will be found studded with dots of 

 blood, and the internal face of the bone also, particularly in apo- 

 plectic subjects. It appears, indeed, that the arteries of the 

 cranium are principally distributed on its external surface, and 

 the veins on its internal surface and diplo. 



In the infant, the diploic veins are small, straight, and have 

 but few branches: in the adult, they correspond with the descrip- 

 tion just given, and, in old age, they are still more considerable, 

 forming nodes and seeming varicose. In children, when the bones 

 are diseased, they partake of the latter character. In order to 

 see them fully, the external table of the skull must be removed, 

 both from its vault and base, with a chisel and mallet. This 

 operation will be much facilitated by soaking the head pre- 

 viously in water for two days. 



SECT. IIT. THE INTERNAL SURFACE OF THE CRANIUM. 



The points for study in viewing the cranium as a whole, are 

 generally the same as have been presented in the detail of each 

 bone. It is, nevertheless, useful to regard the structure in its 

 connected state, as new views are thus presented of the rela- 

 tive situation of parts, and of the formation of the several fossae 

 and cavities. 



The cavity for containing the brain is regularly concave 

 above, and is there called the arch or vault; but below, it is di- 

 vided into several fossae, and is called the base. 



The whole cavity is lined by the dura mater, and, in the adult, 

 presents round superficial depressions made by the convolutions 

 of the brain. These depressions are seldom deep enough to pre- 

 vent the internal periphery of the vault and sides of the crani- 

 um, from being nearly parallel with their external surface. 



On the Vault, or arch, are to be seen, on the middle line, the 

 frontal spine, extending from the ethmoid bone halfway or more 

 up the os frontis: also, the gutter for the longitudinal sinus lead- 

 ing from this spine along the sagittal suture, and terminating at 



