Cm_ 



IV. THE MAMMALIAN NERVOUS SYSTEM 



1. Introductory Topics 



30. The directions which follow can be applied to any of the 

 larger mammalian brains. If human brains are available in 

 sufficient numbers, these alone may be used; but in case the 

 available human brains are insufficient in number or poorly pre- 

 served, the gross dissections may be made on brains of the sheep, 

 dog, or cat. The brain of the sheep is advised. Heads of 

 freshly killed lambs can usually be procured from the butchers. 

 As soon as possible after the killing the brain should be re- 

 moved and hardened for a few days before use by immersing it 

 in a 10 per cent, solution of commercial formalin in water. In 

 this solution it may be preserved indefinitely. 



To remove the brain, first loosen the top of the skull with a 

 saw and chisel. Hold the head firmly in a vise dorsal side up. 

 First with a saw make a transverse cut from 5 to 10 mm. deep 

 across the top of the head about 1 cm. behind the anterior 

 borders of the bony orbits. Then along each side of the head 

 make an obliquely longitudinal saw cut, beginning just above 

 the occipital condyles and extending forward across the 

 dorsal surface of the head about 2 cm. medial to the inner 

 border of the bony orbit. The lines of these two cuts should 

 follow the curvature of the head and meet in the mid- 

 dorsal plane about 2 cm. in front of the transverse cut al- 

 ready made and the saw should be inclined about 45 degrees 

 downward and inward. Avoid cutting so deeply as to enter the 

 brain substance. Then make a very shallow transverse cut 

 through the cranium immediately above the occipital condyles. 

 With chisel and mallet clip through the occipital condyles be- 

 hind the cut last made, and also break the remaining bridge of 

 bone medially of each bony orbit. The top of the cranium 

 may now be pried loose with the chisel and lifted off. The dura 

 mater should be cut around with scissors along the line of the 

 cut surface of the skull and the ventral part of the dura left 

 attached to the skull floor. Lift up the brain from the cranial 



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