Practical Course. 105 
shoulder and wings. The brachial plexus is formed by the junction of - 
the posterior cervical and the anterior thoracic spinal nerves. By clear- 
ing away the tissues in the repion of the kidneys you will be able to 
see the lumbar plexus and the sciatic plexus, which arise from the lumbar 
and sacral vertebra respectively and supply nerves to the leg. 
Separate the head and neck from the rest of the body by cutting 
through the base of the neck. Skin and then cut away the back of the 
head carefully with a knife, so as not to injure the brain, which lies 
immediately beneath the bone. Pick away the sides of the skull so as 
to expose the whole of the brain, and cut away-the dorsal arches of the 
vertebral column with scissors. Lift up the brain from behind with 
as much of the spinal cord attached as possible. Cut through the 
bumerous nerves which pass out through the skull below, so as to 
remove it completely, Examine it under water with a lens and make 
out the following parts :— 
(1) The spinal cord, which fills the canal above the back-bone and 
passes up into the skull by the large hole (foramen mag- 
num) behind. 
(2) The medulla oblongata or expanded part of the spinal cord 
after it enters the skull. 
(8) The median striated lobe (cerebellum), which overhangs the 
medulla oblongata above. 
(4) The large smooth cerebral hemispheres, which occupy almost all 
the upper part of the cavity of the skull and meet each 
other down the middle in a straight suture. 
(5) The olfactory lobes, which are two little protuberances in which 
the cerebral hemispheres terminate in front. From these the 
olfactory or first nerves are given off to the nasal sacs. 
(6) Between the cerebral hemispheres and the cerebellum lies a small 
lobe known as the pineal body ; this, however, is so mych 
overhung by the cerebral hemispheres that you will pro- 
bably be unable to make it out. 
Now turn the brain over in the water and on its ventral surface 
observe— 
(1) The lower surface of the cerebral hemispheres in front. 
(2) The large rounded optic lobes which lie one on either side below 
and behind the cerebral hemispheres. They are connected 
with each other by the large optic tracts which pass in- 
wards from each optic lobe and crossin the middle line 
before giving origin to the enormous optic, or second 
nerves which supply the eyes. 
(8) The infundibulum, which lies in the middle line immediately 
behind the junction of the optic tracts. It is connected 
with the pituitary body, which lies below. 
