1869.| THE MALLEUS AND THE INCUS OF THE MAMMALIA. 403 
Thus I find myself compelled to dissent from every one of Prof. 
Peters’s conclusions ; but, in working over the ground again, I have 
also been led to depart from the Reichertian view (which I have 
hitherto adopted) in one point, and that a very important one. 
In a young mammalian foetus, Meckel’s cartilage passes, above, 
directly into the malleus ; and at no time is any articulation developed 
between the malleus and the rest of the cartilage. Further, the in- 
cus articulates by a broad surface with the malleus, and its dimen- 
sions are such that its long axis appears to continue that of the mal- 
leus and Meckel’s cartilage. In fact it appears exactly as if the 
incus were the proximal end of the cartilage of the first visceral arch. 
If so, the articular surface between the inmeus and the malleus must 
needs answer to that between the quadratum and the articulare of 
the Sauropsidan; and as the incus and the malleus ossify, nothing 
can seem closer than the resemblance which they bear to the quadra- 
tum and the articulare respectively. Hence Reichert conceived 
that the quadratum was the homologue of the ineus, and the malleus 
that of the articulare, and I have foilowed him. But the study of 
Sphenodon and of the Crocodile has led me to believe that we have 
fallen into an error. 
It is admitted, on all hands, and indeed cannot be disputed, that 
the stem and fenestral plate of the stapedial apparatus of the Sau- 
ropsidan answer to the crura and fenestral plate of the stapes of an 
ordinary mammal. But the ineus of a mammal is related to the 
stapes on the one hand, and to the walls of the tympanic cavity on the 
other, nearly as the suprastapedial of a Crocodile is to the same parts ; 
if the zncus remained cartilaginous the resembance would be complete. 
On the other hand, in the human feetus, the stapes has a cartila- 
ginous prolongation which is embraced by the stapedius muscle, and 
contributes to reduce the interval between the stapes and the upper 
extremity of the cartilaginous styloid process (or upper end of the 
hyoidean arch) to a very small space. 
Thus, in the Mammal, the proximal end of the hyoidean arch is 
in nearly the same condition as in the Crocodile, except thae— 
(1) There is a distinct articulation between the suprastapedial part 
and the stem of the stapes. 
(2) The extrastapedial portion of the ‘stapes is no longer distin- 
guishable, and the séapes has lost its direct connexion with the tym- 
panic membrane. 
(3) The suprastapedial is ossified and converted into an incus. 
The zncus, therefore, cannot be the homologue of the quadratum. 
If this view be correct, it follows that as the malleus is the ossified 
proximal end of the cartilage of the first visceral arch, the madleus 
must represent the guadratum. 
And thus the difference between the Sauropsidan and the Mammal 
will be, that in the latter the cartilage of the first visceral arch does 
not become jointed, and does not develope any representative of the 
articulare ; while it gives off an extrastapedial process, which becomes 
connected with the middle of the tympanic membrane. 
Thus, in principle the Reichertian doctrine still holds good ; but 
