210 
PROGRESS OF MICROSCOPICAL SCIENCE. 
and that of the lower edge of the same joint from the inco-stapedial 
joint 4-6 millimeters. 
Stirrup. — The length averaged 3 • 7 millimeters ; the breadth, 
measured from the middle of both limbs, 2 • 3 millimeters ; the distance 
of the upper arch of both limbs to the base of the anterior limb 
2 * 2 millimeters, to that of the posterior limb the same. The breadth 
of the anterior limb averaged 0-6 millimeter, of the posterior 0*8 
millimeter. The length of the base was 3 millimeters, the breadth 
1 • 5 millimeter. 
The tensor tymjpani is inserted into the manubrium generally to 
the extent of from * 7 to 1 • 0 millimeter in breadth. The manner 
of its insertion was found to be very different. In nineteen cases it 
was inserted on the anterior surface, in twenty cases on the inner edge 
and anterior surface, in seven cases on the inner edge alone, in two 
cases on the inner edge and posterior surface, in two cases on the 
posterior surface alone, and in ten cases the tendon passed round the 
inner border, and was fastened on both the anterior and posterior 
surfaces. 
The stapedius had an average length of tendon, measured from the 
summit of the pyramid to its insertion into the stapes, of 1 * 2 milli- 
meter. 
In reference to Dr. Pritchard's paper, which is of considerable 
length, and may be read in the ' Proceedings of the Eoyal Society ' (No. 
168), we shall merely give the author's observations on the development 
of the organ of Corti, and his mode of preparation. He states that the 
organ of Corti is developed from certain of the epithelial cells lining 
the ductus cochleae, which at first consist of a single layer of cuboid 
cells ; later on, those cells which line the floor and sides of the canal 
elongate into the columnar form, while those lining the inner part of 
the floor become longer still, and their nuclei multiply two, three, 
and fourfold. On the outer side of these are five cells, from which the 
chief part of the organ is developed ; these he terms the five primary 
cells. The limbus is next developed and the sulcus formed, the latter 
being completely filled up by the tall columnar cells with proliferated 
nuclei; these, however, dwindle down again as age advances. The 
contents of the first or innermost of the five primary cells are divided 
into two transversely, the upper division forming the inner hair-cell, 
the lower a nuclear cell. The same change takes place in the third, 
fourth and fifth primary cells, their upper division forming the outer 
hair-cells, and the lower the cells of Deiters. The rods are developed 
from the second primary cell, which does not divide transversely, but 
widens at its base so as to form a triangular cell, the inner and outer 
sides of which thicken and form the rudimentary inner and outer rods. 
As this widening increases, the protoplasm disappears from the centre, 
forming the triangular tunnel, and the nucleus divides into two, one 
for each of the lower angles of the tunnel. The rods enlarge at their 
upper and lower extremities, but do not attain their perfect form until 
after birth ; at this period the angle of the inner-rod head has not 
been developed, besides which the shafts are much thicker and more 
clumsy in form than in adult life. The membrana reticularis is 
