355 
of the Ornithorhynchus Hystrix. 
opening between the two nostrils. The structure of the organ 
is shown in Plate XI. 
The external opening of the ear is large enough to admit the 
end of the finger ; the meatus takes the same sweep as in the 
paradoxus; just before it reaches the membrana tympani, it 
contracts to the size of a crow-quill, then again dilates, forming 
a cavity round the membrana tympani : it is lined with hair, 
till it forms this constriction. 
The membrana tympani is externally concave, and is covered 
by a cuticle. It is of an oval form ; the long axis of the oval is 
_±_ of an inch, the short one -2-. Its centre is attached to a small 
bone, connected with the bony rim by which the circumference 
of the membrane is supported : this bone corresponds to the 
malleus of the quadruped. On the inner side of this, and united 
to it by a smooth surface, is a small bone, in the form of a 
trumpet, which may be considered as the stapes, as it fills the 
opening of the foramen ovale. 
There is no perfect cochlea, as in quadrupeds in general ; but 
there is the imperfect cochlea met with in the bird, which has 
been accurately described by Mr. Cuvier.* It consists of a 
conical cavity, a little bent, in the middle of which there is a 
double cartilaginous septum : the two laminae unite before they 
reach the end of the cone; by this means, the surrounding cavity 
becomes a spiral canal, one end of which opens into the vesti- 
bulum, the other terminates at the foramen rotundum. 
The male organs of generation bear a close resemblance to 
those of the paradoxus. The testicles are in every respect similar : 
the vasa deferentia open into the urethra, close to the neck of 
the bladder, as is seen in Plate XII. and it is at the same part 
they open in the paradoxus. 
* Lemons 4’ dnatomie compares, Vol, II, p. 464.0 
