318 JOURNAL OF COMPARATIVE NEUROLOGY. 
by ligament to the relatively long stapedial process of the 
squamosum. 
That the relation of ligament to squamosum is a primary 
condition in this form and not a secondary modification, is seen 
in tracing the development of these structures. In an embryo 
Ig mm. in length (Fig. 2), the ossification of the squamosum is 
just beginning as a formation ina group of cells located upon 
the external semicircular canal of the ear. It extends down 
over the otic process of the quadratum covering with its lower 
(cephalic) end the upper end of a bone which is developed upon 
the external surface of the quadrate. At this stage, the oper- 
culum is just beginning to chondrify as a distinct center, and 
from it a cord of cells is continued forward, ventral to the vena 
jugularis and the ramus jugularis, to the cell surrounding the 
developing squamosum, becoming continuous with them a short 
distance (50y) back of the processus oticus quadrati. The cells 
are of course continuous with those of the squamosum and also 
with the cells between that bone and the quadratum, so that the 
squamosum, the quadratum, and the ligament-anlage, may be 
said to be joined together by a common mass of cells. In the 
just hatched larva, likewise, the ligament-anlage, clearly goes 
to the under side of the squamosum and inserts itself between 
that bone and the processus oticus quadrati, so that it might be 
interpreted as going to both structures. As soon as the con- 
nective tissue fibers develop, however, the relation is seen to be 
with the squamosum and not with the quadratum. It is inter- 
esting to note the relatively early development of the ligament 
—practically at the same time as the squamosum and the oper- 
culum—later, however, than the chondrification of the chon- 
drocranium. 
Spelerpes bilineatus. In this form, as well as in Desmog- 
nathus, the suspensorio-opercular connection possesses the same 
relation to the nervus facialis—that is, the nerve lies entirely 
cephalad and ventrad to the stilus columellae; in other words, 
under it. In relation to the jugular vein, the stilus possesses 
the same relation as the ligament described in Necturus—i. e. 
it passes ventrad to it. 
ee 
