OSSICULA AUDIT US IN THE HIGHER MAMMALIA. 
15 
perforated stapes this artery exists always in embryonic and occasionally in adult life. 
It has some particular relation to Rathke’s arches, which I have not as yet thoroughly 
worked out. I had thought at first that it was the artery to the hyoidean arch, in 
which case it would have afforded strong presumptive evidence in favour of the stapes 
being a part of the cartilage of this arch; but the careful tracing of the artery in the 
embryo Rat and its distribution to the maxillary arch made me forego the idea. 
In older embryoes the stapes approaches and appears to indent the periotic wall 
(Plate 54, fig. 9; and Plate 57, fig. 27), the cellular ring being as yet uniform in its 
dimensions. In Rat embryoes 2 centims. in length the ring has lost its uniform 
character, the basal portion being much larger than that which comes into relation 
with the long crus of the incus ; it is also in a line with the cartilaginous wall of the 
labyrinth, with which it appears to be almost continuous (Plate 57, fig. 30) ; it is 
separated from the vestibular portion of the membranous labyrinth by the remains of 
its primitive wall. The stapes in embryoes before birth has assumed somewhat of the 
appearance and proportions of the adult stapes—it has a well-marked head, two crura 
and a base, which is still separated from the membranous labyrinth (vestibular 
portion) by connective tissue (Plate 58, fig. 37); there is also a well-marked articu¬ 
lation between its head and the long crus of the incus, similar to what exists between 
the malleus and incus; the wall of the cochlea ventrad of the stapes is circular in 
outline and bulges externally, so that the stapes appears to be buried in the wall 
(Plate 57, fig. 32; and Plate 58, fig. 35). 
On examining the stapes of the adult Rat with the lens it is found to bear a very 
close resemblance to the form of the human stapes, differing only in point of size 
(Plate 58, fig. 40, A). 
It has a well-marked head, at the junction of which with the posterior crus is a slight 
tubercle for the attachment of the stapedius muscle. Of the two crura the anterior 
descends from the head to the base almost vertically, the posterior being the more 
curved; the base projects beyond the crura and it is wider, the head, crura, and base 
are fluted internally so that the adult stapes is the merest outside form or semblance 
of bone, a change which takes place after birth. 
The stapedius muscle agrees in its development with the tensor tympani muscle, or 
with any other in the region of the head. The tubercle on the posterior crus has the 
same relation to this muscle that the processus muscularis of Hyrtl has to the tensor 
tympani (the muscle is seen in Plate 57, fig. 34; and Plate 58, figs. 37, 38); it lies 
some distance internal to the hyoidean cartilage, from which it is separated by the 
seventh nerve. The nucleus in its tendon, named inter-hyal by Professor Parker, is 
not present in any of the embryoes from which my sections have been made; more¬ 
over, it cannot have any relation to the hyoidean cartilage, or it would agree with it 
in its developmental history. When the nucleus in the tendon of this muscle is 
present it may be looked upon as comparable to the nuclei found in the tendons of 
other muscles. 
