I 2 
RICHARDS. 
across the auditory canal so as fully to expose to view 
(and to the photographer's camera) the outer surface of 
membrana tympani shown in the illustration and to divide 
the bony septum between the Fallopian and auditory canals. 
In making the section the extreme tip end of the short 
process of the anvil was cut across close to its point of 
articular insertion, and in this and other manipulations of 
the bone a fragment of this septum, about 1 centimeter 
long, 4 or 5 millimeters broad, and 1^ millimeters thick, 
and constituting a portion of the party wall between the 
Fallopian canal above and the chamber containing the 
ossicles below, became separated and rode upwards and 
forwards from its normal position. This fragment is seen 
in the picture lying directly above the body of the incus. 
Of an accident which was the chief cause for the breaking 
away of this fragment I shall have occasion to speak when 
I come to the description of Fig. 3 and Fig. 4. 
Returning now to the description of Fig. 2. — The 
direction pursued by that portion of the Fallopian canal 
which is shown in this picture was found to be nearly hori- 
zontal, declining but little in a downward direction as it 
proceeded backwards to its termination at the stylo-mastoid 
foramen. Its average diameter throughout this part of its 
course is about 5 millimeters ; its length is 55 millimeters. 
The total length of the canal I am unable to state, for in 
the dissection that exposed the cavity of the vestibule the 
anterior and upper wall of that part of the nerve channel 
(not shown in the illustration) which curves downwards 
and towards the median line in front of and above the 
tegmen tympani had been removed. This direction of 
downward and forward curvature in the canal begins at a 
upon. The upper section ran along a line parallel with the left (mesial) 
border of the specimen and leading directly upwards from the stylo-mas- 
toid foramen; the lower section ran along a line extending upon the 
surface obliquely downwards and outwards from this foramen to the lower 
border of the bone. 
