224 THE AMERICAN NATURALIST. [VOL XXXIII: 
rod, smaller than the body, which extends backwards and slightly 
downwards to the stapes. From the body of the malleus a 
strand of cartilage has extended backwards and has fused with 
the manubrial cartilage noticed above, the whole forming the 
manubrium of the adult. Distally, the mallear cartilage is still 
continuous with the rest of Meckel’s cartilage, extending into 
the lower jaw. 
At this stage we can recognize clearly the three! ossicles 
and their processes of the adult ear. So far they all lie outside 
of, and, so far as incus and body of the malleus are concerned, 
in front of the tympanum; they are prespiracular. Hence it 
follows, as certainly as any morphological conclusion can be 
drawn, that they cannot be homologized with the columella and 
its derivatives in the sauropsida, as has been attempted by 
Albrecht, Dollo, and others. This lack of homology is still 
further emphasized by the course of the chorda tympani, which 
in its course passes de/ow the articulation of incus and stapes, 
and then forward on the inner or medial side of the incus to 
the fifth nerve. It may, however, be possible that the manu- 
brial portion of the malleus is homologous with the distal portion 
of the columella. eee 
The question now comes up for decision, What are the hom- 
ologues of incus and malleus in the lower vertebrates? All 
recent students are in agreement that the body of the malleus 
is derived from Meckel’s cartilage, for it retains its connection 
with the cartilage of the lower jaw for some time; but whether 
it is the articulare of non-mammalian groups can only be de- 
cided later, after a discussion of the incus. Concerning this 
latter bone two views are held at present, for no recent student 
has attempted to recognize in it the hyomandibular. Accord- 
ing to one view the incus is the quadrate, while according to 
the other it arises from the proximal end of Meckel’s cartilage, 
while the quadrate, according to this same view, has fused with 
or has become lost in the squamosal region of the mammalian 
skull. 
The greatest objection which has been advanced to the first 
1 The os-obiculare or lentiforme occurring between the incus and stapes is a 
later structure without morphological significance. 
