592 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Hertwig, following Rabl, has given as his main reason for considering the 
stapes to be in part a derivation of the hyoid that the innervation of the 
M. stapedialis is from the seventh nerve. Moreover, the stapes is perforated 
by a branch of the carotis interna. Kingsley has stated that the malleus 
and incus are obtruded into the tympanic cavity from in front, i.e. are 
pre-spiracular, while he leaves one to infer that the stapes is obtruded from 
the back. Disregarding the lack of accuracy involved in such a statement, 
it appears that in the position of the stapes and in its relationship with the 
visceral arches we have to deal with a problem which is complicated by an 
enormous amount of shifting of position that has occurred during the 
growth of the embryo, and that such a statement is not an answer to our 
question. F uchs has come to the conclusion that the stapes is derived from 
the wall of the auditory capsule. With that view, which was the earlier 
view of Parker, Gaupp agreed in his earlier papers. More recently he has 
come to doubt the strength of that position. Hertwig concludes that the 
stapes is in part derived from the auditory capsule, and in part from the 
hyoid arch. 
Opposed to the arguments derived from the position of the stapes are 
the arguments of Rabl as to the nerves, and the argument drawn from the 
position of the arteria stapedialis. Miss Platt has stated clearly that muscles 
are phylogenetically older than the skeletal elements. The primitive con- 
dition, then, shows the muscles inserted into the integument, at which points 
cartilaginous bars were later developed. Now, in none of the embryos of 
from four to seven weeks is there any indication of a stapedius muscle. 
The first appearance that I have found of this muscle is in an embryo of 
about three months (fig. 12). I have studied no individuals of ages between 
seven weeks and three months, so that I do not know the exact time when 
the muscle appears. But inasmuch as the muscle appears very much later 
than the skeletal elements, and since even at four weeks the muscles of 
the neck are indicated, it would seem that as a diagnostic character the 
muscle is of small value — at least, not to be compared with arguments from 
relative position. 
Inasmuch, then, as the stapedialis muscle is innervated from the seventh 
nerve, and since the whole argument hinges on this point, I believe that, 
unless we have stronger corroboration, the fact that the stapes and N. 
facialis are related in this way must be regarded in the light of secondary 
evidence. 
The internal carotid may be seen in figs. 1, 2 and 3, just skirting the 
auditory capsule, running cranio-caudally between the capsule and the first 
pharyngeal pouch, ventral to the latter. Just as it is about to pass the 
