CHONDROCRANIUM OF EUMECES 151 
because the membrane in Lacerta is developed in an entirely 
different position (“‘an ganz anderer Stelle’) from that in the 
mammal. While the mammalian membrane is attached wholly 
to the capsular rim of the fenestra cochleae, that of Lacerta is 
stretched from the rim of the fenestra to the edge of the basal 
plate. ; 
In stage 6 of Eumeces the conditions are so modified as to 
suggest a slightly different interpretation and a closer homology 
with the mammals. Here (fig. 15) there is a less definite con- 
nection of the closmg membrane with the basal plate—more of 
a tendency to close the entire fenestra cochleae with a single 
slightly convex sweep of membrane, only loosely connected with 
the basal plate. In the region of cartilaginous closure of the 
median aperture (fig. 13) the membrane is highly developed in 
this stage. It should also be noted that this membrane conforms 
very closely to the general contour of the ear capsule, so that the 
developing saccus perilymphaticus is almost as strictly intra- 
capsular in this stage of Eumeces as in the mammal. It will be 
readily seen that this interpretation greatly restricts the extent 
of the recessus scalae tympani as an open space of the fissura 
metotica, external to the otic capsule; for, in the entire region of 
the fenestra cochleae, the otic capsule (formed here of connective 
tissue instead of cartilage) and the basal plate must be considered 
as practically in contact. In front of the fenestra cochleae the 
fissura metotica expands again to a considerable cavity, filled 
only with a rather loose and undifferentiated connective tissue 
and containing neither nerves nor important vessels. 
The above considerations indicate that the homology of mam- 
mal and reptile in this point is closer than was held by Gaupp in 
his paper of 1900, but the argument may be carried a step further. 
In the same paper Gaupp advanced the hypothesis that a primi- 
tive fenestra cochleae of the mammal, exactly equivalent to that 
of the reptile, secondarily divides to form the definitive fenestra 
cochleae (foramen rotundum) and the aquaeductus cochleae. 
This surmise has been brilliantly confirmed by his own work on 
Echidna (’08 a), in which the primitive reptilian character is 
JOURNAL OF MORPHOLOGY, VOL. 34, NO. 1 
