192 
PRODUCTION OF SPEECH 
follows. An immediate center, apparently without connection 
with higher sense nerves, controls the simplest reflexes in 
which mainly the organs of the stimulated portion are in¬ 
volved. The sensory nerves, however, send communications 
to many centers of other levels and to the highest centers. 
The higher the center the greater its expanse of irritation 
and control; it controls not only the muscles of its own 
level but also those of lower levels and thus brings, about 
complicated activities. The highest centers act only by stim¬ 
ulating lower centers ; they are, however, in direct connec¬ 
tion with the higher sense-centers, so that single irritations 
from these may be followed by highly complicated activities. 
The relations and connections of various portions of the 
brain are shown in the schematic Fig. 70 after Auzoux’s 
model. 
The spinal cord S at its upper end becomes the bulb B. In 
the dorsal portion (to the left in Fig. 70) of the bulb, there 
are groups of cells — 4 centers ’ — that control various com¬ 
plex muscular activities. The bulb contains the centers of 
coordination and reflex action for chewing, swallowing, action 
of the vocal cords, coughing, etc. It also contains the auto¬ 
matic center for breathing. The ventral portion of the bulb 
is occupied by nerve fibers. 
Just above the bulb lies the pons (Fig. 70, P) and behind 
it the cerebellum (Cl). Overlapping the whole is the cere¬ 
brum ( O), which consists of two hemispheres, a section through 
one of them being shown in the figure. The various portions 
known as the frontal, parietal, occipital and temporal lobes are 
indicated by the letters FL, PL, OL, TL (see also Fig. 57). 
Among other functions the pons has that of transmitting 
the speech impulses from the voluntary centers to the lower 
ones ; some diseases of the pons alter the length of syllables, 
producing what is known as ‘scanning speech.’ The cere¬ 
bellum has no known speech function. The higher portions 
of the brain (stalk, thalamus, corpus striatum, inner capsule, 
etc.) are all to some degree involved in the muscular move¬ 
ments of speech.