1908-9.] Development of Auditory Ossicles in the Horse. 591 
pharyngeal pouch. Fuchs has nowhere figured or modelled the exact shape 
of this pouch as I have found it in the horse. The cranial reflexed portion 
which I have marked with an asterisk does not appear in his work. But 
the stapes anlage is in a very important position with regard to this portion 
of the first pharyngeal pouch. This position I have attempted to show in 
text fig. 4. 
It will be recalled that the stapes is related through mesenchyme to 
two distinct structures, the hyoid cartilage and the incus. This connec- 
tion between the hyoid and stapes represents the hyostapedial ligament of 
Huxley. Fig. 4 shows a model of the auditory ossicles of an embryo of 
seven weeks. It will be here seen that there is no such connection (marked 
** in figures). In the stage represented in fig. 4 the entire auditory 
apparatus was cartilaginous. In an embryo of six weeks the same parts 
are of very young cartilage, and no hyostapedial connection is evident. It 
therefore seems plain that this connection never reaches the state of 
cartilage. Moreover, as Fuchs has shown, the distal end of the hyoid 
cartilage, as shown in figs. 1, 2, and 3, is not the true distal end, but the 
cartilage grows somewhat more dorsal than that point. The connection 
between hyoid and stapes, then, is to be considered as never attaining the 
dignity of a skeletal element. Moreover, a study of the drawings of the 
model and of fig. 11 will show that the stapes lies between the seventh and 
fifth nerves, while the hyoid arch lies between the seventh and ninth. The 
trigeminus ganglion has been omitted from the drawings of the models for 
the sake of simplicity, but it is shown clearly in fig. 11. In other words, 
the connection between stapes and the hyoid bar crosses the seventh nerve. 
This is shown in figs. 1 and 3. 
But that being true, there is no other possibility than to regard, with 
Fuchs, the hyostapedial ligament as a structure whose relation to the 
auditory ossicles must be purely secondary. It appears the more evident 
when certain histological characters are considered. An examination of the 
figures will show that the area marked in the figures ** is histologically 
different from the surrounding mesenchyme. This point has been amply 
dealt with by Fuchs. 
From the foregoing it is evident that the stapes has nothing at all to 
do with the second visceral bar. It is now pertinent to examine it with 
regard to its relations with the second visceral arch. We have seen that in 
its topographical relations the stapes shows characteristics which would 
seem to preclude the possibility of its being a product of the second arch — 
in that it lies medio-dorsal to the first visceral pouch, and between the 
seventh and fifth nerves. 
