74 NERVOUS SYSTEM. 



vibration ; and this vibration being communicated to the brain might, 

 after heavy blows, derange its functions more even than a wound in- 

 flicted by a sharp instrument. To obviate this, in some measure, the 

 helmet has been covered with horse-hair ; an arrangement which ex- 

 isted in the helmet worn by the Roman soldier. There can be no doubt, 

 moreover, that being bad conductors of caloric, and forming a kind of 

 felt which intercepts the air, the hairs may tend to preserve the head of 

 a more uniform temperature. They are likewise covered with an oily 

 matter, which prevents them from imbibing moisture, and causes them 

 to dry speedily. Another use ascribed to them by M. Magendie, 1 is 

 more hypothetical : that, being bad conductors of electricity, they 

 may put the head in a state of insulation, so that the brain may be less 

 aifected by the electric fluid ! 



It is unnecessary to explain in what manner the different layers of 

 which the scalp is composed; the cellular membrane beneath; the pan- 

 niculus carnosus or occipito-frontalis muscle ; and the pericranium 

 covering the bone, act the parts of tutamina. The most important of 

 these protectors is the bony case itself. In an essay written by a dis- 

 tinguished physiologist, 2 we have some beautiful illustrations of the 

 wisdom of God as displayed in the mechanism of man, and of his skull 

 in particular; and although some of his remarks may be liable to the 

 censures that have been passed upon them by Dr. Arnott, 3 most of them 

 are admirably adapted to the contemplated object. It is impossible, 

 indeed, for the uninitiated to rise from the perusal of his interesting 

 essay, without being ready to exclaim with the poet, "How wonderful, 

 how complicate is man ! how passing wonder HE that made him such!" 

 Sir Charles Bell attempts to prove, that the best illustration of the form 

 of the head is the dome ; whilst Dr. Arnott considers it to be " the 

 arch of a cask or barrel, egg-shell, or cocoa-nut, &c., in which the tena- 

 city of the material is many times greater than necessary to resist the 

 influence of gravity, and comes in aid, therefore, of the curve to resist 

 forces of other kinds approaching in all directions, as in falls, blows, 

 unequal pressures," &c. The remarks of Dr. Arnott on this subject 

 are just ; and it is owing to this form of the cranium, that any blow 

 received upon one part of the skull is rapidly distributed to every 

 other ; and that a heavy blow, inflicted on the forehead or vertex, may 

 cause a fracture, not in the parts struck but in the occipital or sphe- 

 noidal bones. 



The skull does not consist of one bone, but of many. These are 

 ioined together by sutures, so called from the bones seeming as if 

 they were stitched together. Each bone consists likewise of two tables; 

 an external, fibrous, and tough; and an internal, of a harder character 

 and more brittle, hence called tabula vitrea. The two are separated 

 from each other by a cellular or cancellated structure, called diploe. 

 On examining the mode in which the tables form a junction with each 

 other at the sutures, we find additional evidences of design exhibited. 



1 Precis Elementaire, edit. cit. i. 177. 



2 Sir Charles Bell, in Animal Mechanics Library of Useful Knowledge, London, 1829. 



3 Elements of Physics, or Natural Philosophy, General and Medical, London, 1527 re- 

 printed in this country, Philad., 1841. 



