CHAPTER VI. 



DISSECTION OF THE BRAIN, OR ENCEPHALON. 



Directions. — The removal of the brain of the horse from its containing 

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

 of the cranial bones. Sup^DOsing the head of an animal recently dead 

 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 interfrontal 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 fosste 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 five per cent, solution of formalin in 

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



MEMBRANES, OE MENINGES, OF THE BEAIN. 



The brain, like the spinal cord, is surrounded by three 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, with 

 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 



