398 PROF. HUXLEY ON THE REPRESENTATIVES OF | May 27, 
outer end of the tympanic cavity ; when it is removed, the proximal 
end of the cornu of the hyoid is seen to expand, and becomes 
converted into a broad plate of cartilage, the curved margin of which 
gives rise to the “scroll.” Internally the plate is continued into the 
stem of the stapes, and speedily becomes ossified (fig. 4). There can 
be no doubt, therefore, that it corresponds with the extrastapedial 
cartilage of the Crocodile. 
What answers to the axehead-shaped suprastapedial cartilage of 
the Crocodile is the upper process of the cartilaginous part of the 
stapes (8. St), which, however, passes into the extrastapedial car- 
tilage externally and above, so as to enclose the foramen, a (fig. 4). 
On the left side, the suprastapedial process was fibrous at the point 6 
(fig. 4). Superiorly, the suprastapedial cartilage (8. S¢) is directly 
continued into the cartilaginous termination of the parotic process 
of the skull (Pe.C), in which granular osseous matter is deposited. 
Thus the suprastapedial cartilage turns out to be nothing more 
than the proximal end of the hyoidean arch, while the stapes and 
its appendages are exclusively related to this arch, and have nothing 
whatever to do with the mandibular arch. 
With respect to the stapes (or columella auris) in Birds, I may 
remark that Prof. Peters makes no reference to the careful investiga- 
tions of Platner (‘ Das Quadratbein der Vogel’), who takes the same 
view of the homology of that structure as himself. 
Platner observes (/. c. p. 16) :—‘‘ The functions of the parts which 
lie within the tympanic cavity of birds almost all bear upon the 
tightening or relaxation of the tympanic membrane. If we consider 
the apparatus directed to this end in the tympanic cavity of Birds, 
we find :—(1) the stapes with the attached cartilage, which represents 
the other auditory ossicles in an aborted condition; (2) the tendon 
of the tensor tympani, which arises from the lower part of the ccciput 
and is attached partly to the stapes and partly to the tympanic 
membrane; (3) an elastic ligament, which I have found in all the 
birds which I have examined, and which passes from the base of the 
cartilage which is attached to the stapes, on the side which is opposite 
to the insertion of the tensor tympani (7. e. from the front aspect), 
up to the tympanal articulation (Paukenhohlengelenk) of the os 
quadratum, where it unites with the mucous membrane which covers 
the tympanic cavity internally.” 
The disposition of the parts described by Platner, in the Common 
Fowl, is shown in the accompanying figure (fig. 5). 
As in the Crocodile, the stem of the stapes is ossified and ends in 
a triradiate cartilaginous expansion. When the skull is horizontal 
one ray of the expansiun is represented by a horizontal triangular 
plate, the outer edge of which is fixed to the tympanic membrane. 
It represents the extrastapedial cartilage of the Crocodile, but 
differs therefrom in being perforated by a large hole. Where the 
stem of the stapes passes into this plate, it gives off a short vertical 
process upwards and a long slender curved process downwards. 
Both these lie free in the tympanie cavity. From the root of the 
upper process an elastic ligament arises and passes forwards to the 
