154 Development of Ear and VII-VIII Cranial Nerves 
it forms at this time a common meeting place into which open the different 
compartments, including the endolymphatic appendage. At six weeks, 
20 mm., the atrium becomes separated into an upper and lower division 
by an ingrowth of its wall, thus forming the utricle and saccule. This 
partition continues inward in such a way as to split the orifice of the 
ductus endolymphaticus, the divided ends of which form the ductus 
utriculo-sacculus. The cochlear pouch opens directly into the atrium, 
and as the development proceeds it can be seen that it is into that part 
of the atrium which is destined to form the saccule. At the fifth week, 
14 mm., a beginning constriction appears between the cochlea and the 
saccular region. This constriction corresponds to the ductus reuniens 
and gradually narrows down until in the adult in many cases the com- 
munication between cochlea and saccule is obliterated. It is very ap- 
parent that the saccule is not developed from the cochlea, but the cochlea 
may be said in a certain sense to develop from the saccule. 
N. VESTIBULARIS AND N. CocHLEARIS. 
The earlier anatomists described the auditory nerve as being made 
up of two main divisions. One of these, according to their plan, supplied 
the utricle, saccule, and the ampulle of the three semicircular canals, 
while the other division they considered to belong exclusively to the 
cochlea. This description prevailed up to the time the exhaustive mono- 
graph was published by Retzius, 84, upon the comparative anatomy of the 
membranous labyrinth and its nerves. This investigator, by means of 
careful dissection of a great variety of vertebrate material, was able to 
present a much more minute description of the n. acusticus than had 
previously existed. In mammals, according to his view, the anterior 
division or ramus vestibularis supplied the utricle, and the superior and 
lateral ampulla, while the posterior division or ramus cochlearis supplied 
the saccule, the posterior ampulla and the cochlea. This classification 
was substantiated not long after by His, Jr., 89, in his paper on the 
development of the human acoustic complex, in which he also represented 
the cochlear division as supplying not alone the ductus cochlearis but 
also the saccule and ampulla of the posterior canal. From that time 
until now the classification made by Retzius has been the one generally 
adopted by both English and German text books. Certain French 
writers (Cannieu, 94, 04, and Cuneo, 99), however, have come back to 
the original conception of the cochlear nerve and its individuality. They 
point out that Retzius fuses in his ramus cochlearis the inferior branch 
of the ramus vestibularis and the cochlear nerve proper. They admit 
