1908-9.] Development of Auditory Ossicles in the Horse. 589 
cartilaginous portion of Meckel’s cartilage — and in no other 'portion of the 
auditory apparatus. 
Inasmuch as there is, even in this early condition, an evidence of a 
separate development of the incus and malleus, the former can have no 
possible connection with the first visceral bar. For the first visceral bar is 
essentially a cartilaginous element and the incus is at all times a separate 
and distinct element. But, on the other hand, the incus is a structure 
derived from the first visceral arch — a condition shown by its position, and 
by its relations with other structures. 
The incus lies lateral to the first visceral pouch and cranial to the point 
of flexure, in the territory peculiar to the first visceral arch. It lies also 
between the seventh and fifth nerves, the course and position of which I will 
describe later. Moreover, the articulation with the malleus is at this time 
a simple hinge articulation — of exactly the type that would he expected in 
a primitive jaw articulation. 
It is therefore evident that the malleus may he a product of the upper 
end of the Meckelian bar but that the incus is not. Fuchs has attempted 
to show that the connection between malleus and the mandibular bar is 
secondary, finding the mandibular articulation distal to the malleus. This 
would tend to corroborate the view of Bardeleben and some others that 
the mammalian lower jaw is a complete homologue of the lower jaw 
of lower forms. That the connection between Meckel’s cartilage and 
the malleus is not secondary and that the malleus is indeed developed 
from the proximal end of the first visceral bar, I shall now attempt 
to show. 
I have already called attention to the fact that the connection between 
Meckel’s cartilage and the malleus anlage was more advanced toward true 
cartilage than any more proximal portions of the products of the first 
visceral arch. Fuchs, in a diagram on page 152 of Arch, fur Anatomic und 
Physiologic, Jahrgang 1905, Supplement-Band, has figured this Meckelian- 
malleus connection as in an earlier condition of development toward 
cartilage than either the malleus-incus anlage or Meckel’s cartilage. My 
investigations do not afford evidence of anything approaching a similar 
condition. It is true that this connection is in an earlier stage than the 
more distal portion of the Meckelian bar, but it is more advanced than the 
malleus-incus portion or than the stapes. Now if the connection between 
the Meckelian bar and the malleus be fully formed in pro-cartilage before 
the malleus has reached a similar stage in its development, it seems im- 
possible to consider that connection as secondarily acquired. Moreover, 
Fuchs has figured in the same diagram an anlage of the true mandibular 
