438 j Julia B. Platt 
posterior opening, there pass a blood-vessel and the nerve oculo- 
motorius. 
The eartilage of the dorsal bar, with that of the vertical bars 
which connect this bar with the trabeeula, forming together the 
erista trabeculae, arises in prochondral tissue that appears to 
be composed of cells which have migrated dorsalwards from the 
prochondral Anlage of the trabecular bar. The cartilage of the dorsal 
bar, however, is not at first connected with the trabecular cartilage, 
but fuses posteriorly with the ascending process of the quadrate 
cartilage before becoming connected with the trabecula by means 
of the cross bars that bound the openings for the optic and ocule- 
motor nerves. In the embryo modeled, the middle bar, although 
represented in fig. 16, was still prochondral. 
STÖHR (80) says that in Triton the orbital wall of the skull 
arises in connection with the trabeculae, and not independently 
as GOETTE (’75) is inclined to think of general occurrence. SEWERTZOFF 
tells me that he considers the independent origin of this dorsal bar 
of cartilage significant as indicating a possible homology with the 
large alisphenoid cartilage, recently described by SEWERTZOFF ('97) 
in the Selachii, or with a similar structure described by SALENSKY 
(78) in Acipenser. 
The quadrate, although primarily connected by procartilage 
with the cartilage of Mecker’s bar, chondrifies independently, and 
at the stage of development represented in fig. 17 (19 mm), has fused 
with the dorsal bar of the crista trabeculae alone. The mandi- 
bular bars, which are paired, even in the procartilage stage (fig. 7), 
are now connected with one another anteriorly merely by procartilage, 
indicated in fig. 15 by the dark band uniting the anterior extremities 
of the bars. 
If fig. 15 be compared with the figure of the adult branchial 
cartilages in Menobranchus (Necturus) given by Huxuey (74), 
it is found that each branchial element already exists as a distinct 
cartilage. Although the meseetoderm of which the prochondral bars 
are formed is of paired origin, the prochondral bars themselves are 
not paired in the hyoid and glossopharyngeal arches, as seen from 
fig. 7. However, when the procartilage is converted into cartilage, 
each cartilaginous element of the arches arises as an independent 
area of chondrification, separated by apa tilage from the neighboring 
cartilaginous elements. 
The body of the axial bar called the »first basibranchial«, 
