172 COMPARATIVE ZOOLOGY. 
is fatal. Of the twelve pairs of nerves issuing from the 
contents of the skull (encephalon), ten come from the me- 
dulla oblongata. Among these are the nerves of hearing 
and taste, and those that control the lungs and heart. 
Respiration ceases im- 
mediately when the 
medulla is injured. 
The spinal cord can 
of itself generate nerve- 
force; but it is mainly 
a conductor—propaga- 
ting through its central 
eray matter the impres- 
sions received by the 
nerves to the brain, and 
taking back through 
its fibrous part the im- 
pulses of the brain. In 
Man, thirty-one pairs 
of nerves arise from 
the cord to supply the 
whole body, except the 
head. Each nerve has 
Fra, 144.—Relation of the Sympathetic and Spinal gn anterior and poste- 
Nerves: e, fissure of spinal cord; a, anterior of . 
a dorsal spinal nerve; p, posterior root, with rior root: its power of 
its ganglion; a’, anterior branch; p’, posterior ‘ 
branch; s, sympathetic; e, its double junction Causing muscular con- 
by white and gray filaments. traction is lodged in 
the former (hence called motor), and the power of giv- 
ing rise to sensation resides in the latter (sensory). The 
fibres leading from the brain to the cord cross one anoth- 
er in the medulla oblongata, so that if the right cerebral 
hemisphere be diseased, the left side of the body loses the 
power of voluntary motion. 
The sympathetic nervous system is a double chain of 
knots, or ganglia, lying along the sides of the vertebral 
