MORPHOLOGICAL STUDIES. 
179 
thelium. This view, which I formerly only mentioned as true 
for the suprabrauchial nerves, I must now also extend to the 
prsebranchial and the sensory part of each postbranchial nerve. 
The ganglion complex has also to acquire its first and per- 
manent connection with the central nervous system, and of the 
mode in which this takes place there can be no sort of doubt. 
The main trunk of the nerve and its connection with the cen- 
tral nervous system are formed respectively by the formation 
of nerve-chains from some of the ganglion-cells, and by the 
growth of fibres into the central nervous system. 
Here again, however, the cranial ganglia present us with 
complications as compared with the spinal. 
It is well known that the whole of the motor fibres of the 
spinal nerves (those to the voluntary and the visceral muscles 
derived respectively from the anterior and lateral horns) pass 
out in the auterior roots. Now, there can be no doubt 
that the whole of the anterior root of a spinal nerve is a 
direct outgrowth from the central nervous system. All 
observers are agreed on this point. Quite other conditions 
obtain in the head. In the oculomotorius, trochlearis, and 
abducens, the only nerves which are comparable at all to ante- 
rior roots of spinal nerves, no fibres are derived from the homo- 
logue in the head of the lateral horn of the spinal cord ; in 
other words, the anterior roots of the head give no fibres to 
visceral muscles, and — a fact which is well known — the fibres 
to the visceral muscles of the head pass out with the posterior 
roots of the cranial nerves. It appears also that these fibres 
take their origin in the continuation of the lateral horn in 
the head. This being so, and it being also true that all other 
motor nerves, including those of the spinal cord and the three 
eye-muscle nerves, certainly occur as outgrowths of ganglia 1 
situated within the central nervous system, it becomes a ques- 
tion whether the motor fibres of the gill-cleft muscles are not 
also direct outgrowths of the central nervous system. I must 
confess that I have not as yet been able to settle this point by 
* See fig. 100, which depicts the third and its central ganglionic origin as 
seen in Lacerta agilis. 
