II. The Cochlea of the Ornithorhy nclins platypus compared with that of ordinary 
Mammals and of Birds. 
By Urban Pritchard, M.D., P.B.C.S., Aural Surgeon to Kings College Hospital. 
Communicated by Professor Huxley, Sec. B.S. 
Received November 9,—Read December 9, 1880. 
[Plates 45, 46.] 
In the course of my researches into the structure of the cochleae of various Mammals 
and Birds, I have been frequently struck with the marked dissimilarities displayed in 
these two forms of the organ. For this reason I naturally became anxious to examine 
it in a Monotreme, and to find, if possible, some links in structure between these two 
cochleae. 
I therefore made inquiries for specimens of the Ornithorhynchus platypus among my 
Australian friends, and, after a year or two’s patience, succeeded in obtaining several 
skulls of that animal in an excellent state of preservation. These have enabled me to 
make some researches into the morphological and microscopical structure of this cochlea, 
the results of which I trust will be deemed worthy of the consideration of the Ptoya.l 
Society. 
Morphology. 
That part of the bony labyrinth which constitutes the cochlea of this animal consists 
of a somewhat curved tube, about 5 inch (6'3 millims.) in length and - 2 ^ inch 
(1*26 millim.) in diameter, projecting from the cavity of the vestibule and embedded 
in the substance of the petrous bone near its anterior extremity (see Plate 45, fig. 1 ). 
This tube is directed almost horizontally forwards and is slightly curved outwards, 
its apex forming a little projection on the outer border of the petrous bone close to its 
pointed end. 
In section this tube is of an oblong form at its commencement, vestibular end, with 
its greatest measurement inch or 2 millims.) from top to bottom (see Plate 45, 
fig. 3). A little further forwards it becomes triangular, but soon it assumes its general 
oval-shape with its greatest diameter inch or 1T5 millim.) from side to side 
(see Plate 45, fig. 2 ). The tube terminates in a slightly enlarged rounded extremity, 
which, however, is not spherical but flattened from top to bottom. Its greatest diameter 
(from side to side) is fr inch or P7 millim. This enlargement is due to the partial 
2 N 
MDCCCLXXXI. 
