74 COMPARATIVE MORPHOLOGY OF VERTEBRATES. 
stapes (fig. 82). In the anurans there is no connection of quadrate 
with stapes, but there is a slender rod, the columella, extending from 
the tympanic membrane to the stapes. This columella arises behind 
the tympanic cavity but with growth is included in it, so that in the 
adult it appears to run directly through it. In the sauropsida the 
relations are much as in the anura, but when ossification sets in, the 
columella may form several elements. In development the columella 
in these forms is directly connected with the hyoid arch. 
In the mammals there is 
a chain of three bones to carry 
the sound waves across the 
tympanic cavity. In the 
fenestra vestibuliis the stapes, 
which connects with an incus 
and lastly comes the malleus, 
which has two long processes, 
a manubrium which is in- 
serted in the tympanic mem- 
brane, and a processus an- 
extends into the petrotym- 
2 panic (Glaserian) fissure 
_ of the temporal bone. That 
ae these parts are not to be com- 
Fic. 71.—Diagram of ear bones of embryo pig, pared to the columella of the 
the tympanic cavity laid open. gg, goniale; 7, sauropsida and anura_ is 
incus; 4j, lower jaw; m, malleus; mk, Meckel’s 
cartilage; mm, manubrium of malleus; s, stapes; shown by the fact that they 
sp squamostl: zygomatic. Theoutinesof tbe invade the tympanic cavity 
dotted. from in front and that they 
are in front of the chorda 
tympani nerve,-the columella of the non-mammals lying behind it. 
The homologies of these parts seem clear. In development the 
malleus is the posterior end of Meckel’s cartilage, being in the position of 
the articulare of lower groups. It articulatés with the incus, which in 
turn at first articulates with the wall of the otic capsule, as well as with 
the stapes, and thus corresponds with the quadrate. The stapes is 
apparently the same throughout the whole of the tetrapoda. It is to be 
noted that many paleontologists deny the homologies recognized here, 
think that in the mammals the quadrate has been lost in the glenoid 
terior (Folian process) which — 
