No. 387.] THE OSSICULA AUDITUS. 221 
tympani, which runs forward adove the shaft of the columella 
and on the medial side of the quadrate, to extend into the lower 
jaw, together with the mandibular branch of the trigeminal 
nerve. With further development the columella seemingly 
invades the tympanic cavity. In reality the cavity in its ex- 
pansion extends around the rod, which, however, remains con- 
nected with the posterior tympanic wall by means of a fold of 
the tympanic epithelium and the enclosed mesenchyma. The 
quadrate, contrary to what obtains in the urodeles, does not 
articulate with the stapes, nor is it connected, except by liga- 
Fic. r.— Section through the tympanic region of an embryo of Scedeforus undulatus, showing 
t i g the tympani ity from behind ; the arrow points towards the tip 
of the snout, the cartilages are black. d, digastric muscle; c¢, chorda tympani; /, facial 
nerve; mz, head of Meckel’: tilage; g, quadrate ; ¢, tympanic cavity. 
he columella, c 
ment, with the sound-conducting apparatus. Its sole function 
is that of a suspensor of the lower jaw. The sauropsidan type, 
then, may be characterized as consisting of a stapes and a colu- 
mella which form the auditory chain, the columellar shaft being 
post-trematic in origin, while the quadrate is outside of and apart 
from the sound-conducting apparatus. 
All other questions regarding this apparatus in the saurop- 
sida must be ignored here — the question of the homologies of 
the stapes, the relations of both stapes and columella to the 
hyoid and hyomandibular, etc., as well as discussions of mus- 
cles; we can only call attention to the fact that there is some 
