CHAPTER VI. 



DISSECTION OF THE BRAIN, OR ENCEPHALON. 



DirectUMs. — The removal of the brain of the horse from its contain- 

 ing cavity is a somewhat difficult operation, in consequence of the 

 thickness of the cranial bones. Supposing the head of an animal 

 recently killed to have been procured for the special purpose, the first 

 steps are the disarticulation of the jaw on both sides, and the removal 

 of the inferior maxilla. Next denude the cranial bones of the muscles 

 and other soft structures, and with the saw remove on each side the 

 zygomatic arch, the supraorbital process of the frontal, and the styloid 

 process of the occipital. Estimating the thickness of the last-named 

 bone at the poll, as much as possible of it may be sawn off without 

 actually encroaching on the cranial cavity. Armed with a chisel, 

 mallet, and strong bone-forceps, the student must now remove as 

 much of the cranial wall as will enable him to extract the brain ; 

 and he may do this by removing either the roof or the floor of the 

 cavity. The first method is the speedier, but the latter has the 

 advantage of permitting the roots of the cranial nerves, the pituitary 

 body, and the cranial vessels to be better preserved. The dura mater is 

 to be left as far as possible intact, but its attachments along the inter- 

 frontal and interparietal sutures, and to the oblique ridge between 

 the cerebral and cerebellar divisions of the cranial cavity, must be cut 

 with the scalpel. When the forepart of the cavity is reached, the 

 handle of the scalpel is to be used to scoop the olfactory bulbs out of 

 the fossae in which they lie. 



The brain having been removed in its membranes, it should be laid 

 with its base upwards on a broad strip of calico, and lowered into a 

 vessel of methylated spirit or a ten per cent, solution of nitric acid in 

 water. After a week's immersion, it will be ready for examination. 



MEMBRAXES, OR MENINGES, OF THE BRAIN. 



The brain, like the spinal cord, is surrounded by thi-ee envelopes : 

 the dura mater, the arachnoid, and the pia mater. 



The Dura Mater is the external of these envelopes. It is a strong 

 fibrous membrane, similar in structure to the spinal dura mater, wdth 

 which it is continuous at the foramen magnum. It differs, however, 

 from the same envelope of the spinal cord, in that it is closely adherent 



