222 THE AMERICAN NATURALIST.  [Vovu. XXXIII. 
evidence to show that that portion of the columella which lies 
within the tympanic membrane may possibly be homologous 
with the manubrium of the mammalian malleus, to be described 
below. 
In speaking of the auditory ossicles of the mammals, it will 
be necessary to go into more detail, since, while the different 
features of development have been described several times, 
there is great diversity of opinion as to the homologies of the 
parts concerned. 
In the pig the ossicula auditus and related parts can first be 
made out in embryos measuring about eighteen millimeters in 
Sass 
h 
Fic. 2. — Diagram of otic region in Sceleporus embryo: c, columella; cz, chorda t tympani; 
J, facial ote. h, as y hm, a ee neye: m hime of Meckel’s cartilage ; 
g, quadrate; 
i 
total length, and sagittal sections give the clearest pictures. In 
embryos of this size the otic capsule has not begun to differ- 
entiate, the utriculus, sacculus, and semicircular canals being 
imbedded in a homogeneous matrix of mesenchyme, which 
nowhere shows that concentration of nuclei so characteristic 
of procartilage formation. The stapes, on the other hand, is 
well outlined as a mass of procartilage formed around the stape- 
dial artery, the mass having the form of a ring rather than 
the stirrup shape of the adult. Ventral to the stapes is the 
Eustachian cleft, which as yet shows no differentiation into 
tympanic cavity and tube. This cleft extends outward for some 
distance above, and parallel to the inner end of the external 
