THE BRAIN 351 



bottom of the bottle, and place the brain upon it, in order to 

 prevent flattening from contact with the glass, and to enswre 

 free access of the spirit to all parts of the surface. 



To remove the brain, first shin the head ; then expose the 

 bra/in by snipping away, with the bone-forceps, the roof and 

 sides of the skull, beginning at the foramen magnum, and work- 

 ing forwards. Take special care in the region of the ears to 

 avoid injury to the floccular lobes of the cerebellwm, which are 

 lodged in the floccular fosses of the periotic bones (p. 282). 



Having completely removed the roof and ' sides of the 

 cranium, and cut through the dura mater, a tough fibrous 

 membrane which lines the cranial cavity, cut across the spinal 

 cord about half an inch behind the foramen magnum, and 

 turn out the brain from behind forwards, lifting it up gently 

 with the handle of a scalpel. 



Note and identify the several nerve-roots as you do so, 

 and cut through them in order, close to the skull-wall, so as 

 to leave as much of the roots as possible attached to the brain. 



Place the brain in spirit at once, handling it with great 

 care, as it is very soft and easily damaged. Leave it in spirit 

 for three or four days, and then dissect it as described below. 



The several divisions of the rabbit's brain are the same 

 as those of the brain of the dog-fish, the most important 

 differences between the two being, (1) the great size of the 

 cerebral hemispheres, which overlap and conceal the dorsal 

 and lateral surfaces of the thalamencephalon and optic lobes ; 

 (2) the greater size and more complicated structure of the 

 cerebellum ; (3) the much greater development of the trans- 

 verse commissures, connecting the two halves of the brain 

 with each other. 



Bemove the hardened brain from spirit, and examine it in 

 a small dish of water or weak spirit. 



A. The Brain-membranes. 



1. The dura mater is the tough connective-tissue membrane 

 which lines the cranial cavity. The greater part or 

 the whole of it is left in the skuU on removal of the 

 brain. It projects into the cranial cavity as a median 



