442 THE HORSE. 
matter, and is a ganglion, superadded for the special purpose of establish- 
ing the respiratory function. From its lower border proceed the filaments, 
which unite to form the hypoglossal nerve, while from the upper side 
emerge the glosso-pharyngeal and pneumogastric nerves. 
THE ENCEPHALON (ey, in, xepady, head). 
THE CEREBELLUM TOGETHER WITH THE CEREBRUM form the mass of the 
encephalon, and they may be examined together with advantage. The 
two completely fill the cavity of the cranium, and are invested by three 
membranes ;—the dura mater, fibrous and strong ; the pia mater, vascular 
and tender; and the arachnoid, a serous membrane of the ordinary cha- 
racter. The dura mater also dips down between the lobes of the cerebrum 
to form a protection against lateral displacement called the falx, and is 
Fic. 3.—VIEW OF THE SUPERIOR SURFACE OF THE ENCEPHALON 
a. Anterior termination of the longitudinal fissure. d. Middle lobe of the cerebel 
b. b. Lateral hemispheres of the cerebrum, e. e. Superior median nes 
c. c. ¢. Corpus callosum. J. g. Membranes covering the spinal cord 
spread across from one petrous bone to the other, constituting the tentorium 
cerebelli, The mass of the encephalon in the horse is small as compared 
with that of man, weighing not quite a pound and a half, while the 
human brain averages three pounds in the male, and four or five ounces 
