72 THE NERVOUS SYSTEM OF THE FROG, 
Chap. VI—THE NERVOUS SYSTEM OF THE FROG. 
The nervous system consists of— 
i, A central portion—the brain and spinal cord—which 
lies in the cartilaginous and bony tube formed by the 
-eranium and vertebral column, and which is the 
centre where sensations are felt, and whence motor 
impulses causing the muscles to contract take their 
origin: and 
ii, A peripheral portion—the nerves themselves—which 
connect the central portion with the skin, sense 
organs, muscles, viscera, etc., and serve to convey 
sensory impulses from these parts to the brain and 
cord, or motor impulses from the central organs to 
the muscles. 
Fig. 11, The nervous system of the edible frog (Rana esculenta), from 
the ventral surface. (From Hcker.) 
F', facial nerve: G, ganglion of pneumogastric nerve: He, cerebral 
hemisphere: Le, optic tract: Lop, optic lobe: M, boundary between 
medulla oblongata and spinal cord: M1-10, the spinal nerves: MS, con- 
nection between fourth spinal nerve and sympathetic chain: N, nasal sac: 
Ni, sciatic nerve: No, crural nerve: o, eyeball: S, trunk of sympathetic; 
S 1-10, the sympathetic ganglia: Sp, continuation of sympathetic into head. 
I, olfactory nerve: II, optic nerve: III, motor oculi: IV, trochlear 
nerve: V, trigeminal and facial nerves: Va, ophthalmic branch of trigemi- 
nal: Ve, maxillary branch of trigeminal: Vd, mandibular branch of tri- 
geminal: Ve, hyomandibular branch of facial: Vg, Gasserian ganglion: Vs, 
upper end of sympathetic trunk, in connection with Gasserian ganglion: VI, 
abducens nerve: VII, facial nerve: VIII, auditory nerve: X, glossopharyn- 
geal and pneumogastric nerves: X1, ramus anterior of glossopharyngeal : 
X2, ramus posterior of glossopharyngeal: X 8-4, branches of pneumogastric. 
