158 Development of Har and VII-VIII Cranial Nerves 
ganglion cells connecting the anlage of the spiral ganglion with the 
brain, and the conversion of this column into fibroblasts produces the 
early fibers of the trunk; this would explain the abrupt appearance of 
the nerve trunk in all parts of its course at once. 
Proceeding to embryos 30 mm. long, the same as seen in Figs. a, b, ¢, 
Plate I, we meet with conditions which are practically those found in 
the adult. There is the vestibular nerve, on whose trunk is situated its 
ganglion mass, consisting of an upper and lower division. ‘The upper 
division is connected with the labyrinth by the branches supplying the 
anterior and lateral ampulle, and the utricle; the lower division gives 
off branches to the sacculus and posterior ampulla. In the adult the 
division between the pars superior and pars inferior is still more pro- 
nounced and the separation can be even seen in the trunk of the nerve. 
The ganglion mass is completely divided except for a bundle of anasto- 
mosing fibers, which according to Alexander, 99, may also be accompanied 
by a chain of ganglion cells—a persistence of the embryonic connection 
between the pars superior and pars inferior. 
The cochlear nerve lies on the median surface of the two divisions of 
the vestibular ganglion, but is connected with them only by contiguity. 
This can be demonstrated by dissection methods in pig embryos; the 
cochlear trunk can be easily lifted off, leaving the vestibular ganglion 
mass and all of its branches in position, both of the pars inferior and 
pars superior. At the point where they enter the central nervous system 
the cochlear and vestibular trunks are in the 30 mm. embryo closely 
united; they run into each other slightly more than is shown in Fig. 5, 
and it is not easy to distinguish at what point the one stops and other 
begins. Their separation is brought about by the increase in size of 
the restiform body which develops in between them. During this process 
it could easily happen that some of the cochlear fibers should become 
grouped in with the vestibular, or that some of the vestibular should 
become grouped in with the cochlear; in both cases finally reaching their 
proper destination. If the individual fibers were traced in a large num- 
ber of cases undoubtedly a considerable variation in this respect would 
be found. An important stride in this direction was made by Held, 93. 
The twisted, rope-like character of the cochlear nerve, as indicated 
in Fig. 5, is easily identified in the 30 mm. embryo. An effort was 
made in the pig to determine the number of turns and their relation to 
the number of turns of the spiral ganglion. There is apparently a 
certain amount of correspondence, but the fibers were too tightly adherent 
to admit of a satisfactory unrolling of the nerve. 
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