LAWS OF LIFE, HEALTH, ETC. 249 
tained in the skull, where it is protected by its bony plates. 
It is divided into the cerebrum, which consists of two lobes or 
hemispheres united in the centre. Externally it is covered by 
the gray matter, which is composed of nerve cells. There are 
deep grooves or convolutions running in irregular lines all 
over the surfaces. This portion of the brain is the seat of the 
special senses and will power. The cerebeilum, or little brain, 
lies under and at the back of the cerebrum. It is also in two 
parts, united in the centre. It is said to control and 
harmonize the movements of the body and limbs. There are 
five cavities in the brain called ventricles. At the base, 
resting on the floor of the skull, are two important parts of 
the brain, called the pons variola and medulla oblongata. 
The pons is the bond of union between tbe parts of the 
brain. The medulla may be reckoned the beginning of the 
spinal cord. From it spring the nerves which control the 
vital forces of lfe—breathing, swallowing, digestion, &e. 
From the medulla the cord passes down the opening at the base 
of the skuil into the bony canal formed by holes in the vertebree 
or backbone; small openings in which allow for the 
transmission of the costal nerves, comprising 31 pairs, which 
convey tke vital impulses to the muscles and parts of the 
trunk, and unite with the nerves coming direct from the brain 
to form phlexuses or network formations of nerves. Thecord, 
when it reaches the bottom of the spine, terminates. The 
nerves that supply the leg are the great and lesser sciatic, 
derived from the sacral plexus. The great sciatic is the 
largest nerve in the body, being at one point about three- 
quarters of an inch broad. It passes down the leg, lying 
embedded among the muscles of the back portion. It divides 
into two branches called the popliteal. One of these is 
distributed principally to the superficial, and the other to the 
deeper parts of the leg and foot. 
The internal organs of the body are numbered from 
above downwards. The lungs, heart, diaphragm, liver, 
stomach, pancreas, spleen, intestines smaller and greater, the 
