George L. Streeter 155 
that these two lie side by side and are closely united, but further than 
that deny any anatomical or physiological relation. A similar conclu- 
sion has also been reached by Alexander, 99, who studied serial sections 
of the acoustic ganglion mass taken from various adult mammals. 
My own observations concerning the development of these structures 
in the human embryo are quite contrary to those of His, Jr., and as will 
be immediately seen, they seem to indicate that the cochlear division 
of this complex has nothing to do with the nerves to the saccule and 
posterior ampulla, but possesses its own specialized characteristics which 
distinguish it from all the rest of the acoustic mass. Embryologically, 
therefore, it seems well to follow Canniew’s, 94, lead and adopt the 
following classification : 
N. Octayvus (N. AcustTIcus). 
r. ampul. sup.. 
pars superior, r. ampul. ext. 
r. recess. utric. 
n. vestibularis, 
F A . sacc. 
pars inferior, Fn Bae 
r. amp. post. 
n. cochlearis, }ramuli spirali. 
The form and branches of the acoustic mass in its different stages and 
its relation to the labyrinth is shown in the figures on Plate I and II. 
Two colors are added so that the cochlear division can be distinguished 
from the vestibular; the former is colored yellow and the latter light 
red. The same ganglion mass is shown more diagrammatically in the 
accompanying Fig. 5, showing its appearance in embryos 4, 7, 9, 20, and 
30 mm. long. The vestibular part is indicated by fine dots and the 
cochlear by coarse dots. The drawings on the left present a median 
view and those on the right a lateral view. 
In the youngest stage, embryos of about 4 mm., Mall collection, No. 
148, the outlines of the ganglion mass are indefinite, particularly the 
peripheral border. The central end is more distinct and the protoplasmic 
cell processes can be seen leading to the wall of the neural tube. This 
is somewhat younger than the earliest stage of His, Jr., 89. In the next 
stage, embryos of about 7 mm., the outlines of the ganglion can be clearly 
made out. A section through such a ganglion is shown in Fig. 6. It 
les closely against the front edge of the vesicle, its lower end migrating 
around on the median side. In its outer form it consists of an upper 
and lower part, pars superior and pars inferior, each of which develops 
its own separate group of peripheral nerve branches; the central root 
11 
