THE ORANIAL NERVES. 81 
Each trunk receives a branch from each of the spinal nerves 
of its side, and at the junction of each of these branches with 
the main trunk there is a ganglionic enlargement. 
The coccygeal or tenth spinal nerve, unlike the others, is 
connected with the sympathetic by more than a single branch : 
the actual number of these branches is not constant, but is 
said to vary from two up to as many as twelve. 
From the sympathetic ganglia nerves are given off to the 
bloodvessels and viscera, the chief ones being :— 
i. The cardiac plexus: formed by nerves arising 
from the first sympathetic ganglion: the plexus 
is a meshwork of nerves on the auricles and 
around the great vessels at their openings into 
the heart. 
ii. The solar plexus: on the dorsal surface of the 
stomach: the nerves are derived mainly from 
the third, fourth, and fifth ganglia. Hepatic, 
renal, genital, hemorrhoidal, and vesical plexuses 
also exist in connection with the liver, kidney, 
reproductive organs, large intestine, and bladder 
respectively. 
III. The Cranial Nerves. There are ten pairs of cranial 
nerves in the frog, which are numbered in order from before 
backwards. 
To dissect the cranial nerves expose the brain by removing the 
rocf of the skull as already described, and then follow the special 
instructions given in the case of the more important nerves. 
1. The olfactory nerve; the special nerve of smell: arises 
from the anterior end and outer side of the olfactory lobe, 
and is distributed to the membrane lining the nasal 
cavity. 
To see its course and distribution dissect from the dorsal surface 
removing the roof of the anterior part of the skull, including the 
nasal bone. 
2. The optic nerve: the nerve of sight: arises from the side 
_ of the brain just below the optic lobe, crosses over partially 
at the optic chiasma on the under surface of the brain, 
and then runs outwards to the eyeball. 
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