32 A MANUAL OF ANATOMY. 



DISSECTION. 



To Remove the Brain. The anterior and posterior portions of the occipito- 

 frontalis and the temporal fascia have been already turned down. The tem- 

 poral muscle is now to be dissected from its attachment to the temporal fossa 

 (the deep temporal vessels and nerves noted, see pp. 117, 121) and turned over, 

 or cut away entirely on a level with the zygoma. With a saw the outer table 

 of the skull is to be cut through in a line from a point three-fourths of an inch 

 above the supra-orbital arches to the occipital protuberance, completely en- 

 circling the head. 



When the outer table has been cut through, as is shown by the bloody saw- 

 dust turned out, the saw is to be changed for a chisel. The ordinary " cold " 

 chisel is suitable for this purpose. With a chisel break off the skull-cap, 

 entering the chisel first at the external angular processes of the frontal bone, 

 then over the mastoid processes. Be careful not to drive the chisel through 

 into the brain. After breaking the skull at these four points, the entire top of 

 the skull will probably be loosened. 



Insert a strong hook at the forepart of the skull-cap, and with a sharp, 

 quick pull tear it from the dura. 



Before going farther study the middle meningeal artery and dura. 



For the artery see page 44. 



The Dura. Figs. 6 and 8. 



The dura is the most external membrane which envel- 

 ops the brain. It is closely applied to the inner surface 

 of the cranium and forms the inner periosteum for the bones 

 which compose it. 



This attached surface is rough, as will be seen after the 

 skull-cap has been removed. The inner surface of the dura 

 is smooth, and is in close relation to the arachnoid (see 

 page 1 5 2), from which it is separated by the smallest inter- 

 val, called the subdural space. 



Offsets from the inner layer of the dura are found in cer- 

 tain places, as between the halves of the cerebrum the falx 

 cerebri, between the cerebrum and cerebellum the ten- 

 torium cerebelli, and between the two lobes of the cere- 

 bellum the falx cerebelli. 



Along the lines where these offsets take place spaces are 



