76 



NERVOUS SYSTEM. 



Fig. 4. 



will generally happen, that a blow, intended to cause serious bodily 

 injury, will be sufficient to break through both tables, or neither. 



Lastly, the dura mater, which has been reckoned as one of the tuta- 

 mina cerebri, lines the skull, and constitutes a kind of internal perios- 

 teum to it. It may also be inservient to useful purposes, by deadening 

 the vibrations, into which the head may be thrown by sudden concus- 

 sions; as the vibrations of a bell are arrested by lining it with a soft 

 material. It is chiefly, however, to protect the brain against itself, 

 that we have the arrangement which prevails. The cerebrum, as well 

 as the cerebellum, consists of two hemispheres; and its posterior part 

 is situate immediately' above the cerebellum. It is obvious, then, that 

 without some protection, the hemisphere of one side would press upon 

 its fellow, when the head is inclined to the opposite side; and that the 

 posterior lobes of the brain would weigh upon the cerebellum in the 

 erect attitude. 



The hemispheres are separated from each other by the falx cerebri, 



in the upper margin of which is the 

 superior longitudinal sinus. The 

 falx passes between the hemispheres. 

 The tentorium cerebello super ext en- 

 sum a prolongation of the dura 

 mater passes horizontally forwards 

 so as to support the posterior lobes 

 of the brain, and prevent them from 

 pressing injuriously on the cerebellum. 

 A process of the dura mater passes 

 also between the hemispheres of the 

 cerebellum. Independently of the 

 protection afforded to the encepha- 

 lon, the dura mater lodges the great 

 sinuses into which the veins discharge 

 their blood. These different sinuses 

 empty themselves into the torcular 

 Serophili or confluence of the sinu- 

 ses; and ultimately proceed to con- 



Falx Cerebri and Sinuses of upper and back gtitute the lateral sinuses, which pass 



part of Skull. through the temporal bone, and form 



1, 2. 3. Section of the bones of the cranium, , . 7-7 



showing the attachment of the falx major. 4! the internal JUgUlar Veins. 



fnfamina QVP rmf nrmfinpfl tn 

 tUtamma are not COnnnCU tO 



Contents of the Cranium. The 



Anterior portion of superior longitudinal sinus. 

 5. Middle portion. 6. Inferior portion ; the outer 



table of the cranium removed 7. Commence- 



ment of the inferior longitudinal sinus. 8. Its .- .. - ... 



termination in the straight sinus. 9. Sinus SDine appears to DC, it pOSSlble, Still 



quartus or rectus. 10. Vena Galeni. 11. One , u J T 1 1 11 



of the lateral sinuses. 12. Torcular Herophili. better protected. In the SKUll, W6 



13. Sinus of the falx cerebelli. 14. Internal firm hnnv Pfl<;p in flip <*r>ir)P 



jugular vein. 15. Dura mater of the spinal See a nrm ? DOn J C3Se 9 ** l Spine, 



marrow. 16. Tentorium cerebeiii. 17, 17. a structure admitting considerable 



Falx cerebri. . c -i ',1 i e 



motion ot the parts, without risk ot 



pressure to the marrow. Accordingly, the spine consists of numerous 

 distinct bones or vertebrae, with fibre-cartilaginous technically called 

 inter vertebral substances placed between each, so that, although the 

 extent of motion between any two of these bones may be small, when 

 all are concerned, it is considerable. The great use of this interver- 



