The Development of the Cartilaginous Skull etc. in Neoturus. 423 
The order of development. 
True cartilage is first found in the embryo 17 mm long, and 
appears in the course of the trabeculae, extending from beneath 
the optic stalks through the antero-lateral margins of the basieranial 
plate. Sröur (80, ’82) tells us that in Triton, Siredon, and in 
the Anura, the cartilage of the visceral skeleton appears before 
that of the trabeculae, or remaining skull. The chondrification of 
the trabecular bars in Necturus is immediately followed by that 
of the prochondral bars in the visceral arches. The bars of the 
mandibular, hyoid, and glossopharyngeal arches chondrify almost 
simultaneously. Those of the vagus arches somewhat later. In the 
meantime cartilage appears in the occipital region of the skull, with 
which the cartilage of the trabeculae in its backward growth 
unites forming the basal plate. The auditory vesicles then become 
gradually surrounded by cartilage, which becomes connected with 
the basal plate through the chondrification of intermediate tissue, 
primarily in the form of two pairs of connecting bridges, which, 
becoming wider in antero-posterior extent, meet and fuse with one 
another, while the anterior extent of the basal plate is further in- 
creased by a third cartilaginous connection with the auditory capsule 
anterior to the facial ganglion. Cartilaginous partitions appear in 
the internal chamber of the auditory capsules with the development 
of the semicircular canals. The trabeculae extend forwards and 
become connected with one another anteriorly by an internasal plate, 
while from each trabecular bar an antorbital process grows laterally. 
The posterior part of the brain becomes roofed by a band of carti- 
lage connected with the dorsal part of the united auditory capsule 
and occipital arch. In no case is the development of one of these 
cartilaginous elements of the skull complete, however, before the 
development of other cartilaginous elements begins. Finally a car- 
tilaginous support for the nasal membrane and a cartilaginous ring 
about the eye arise independently, while a number of fusions occur 
between cartilaginous elements originally separate. 
The basal plate1 
The cartilage first found on each side of the head in the course 
of the trabeculae, is separate from every other skeletal element, 
1] distinguish the prochondral plate lying below the brain, from the 
cartilaginous plate found here in later stages of development, by calling the 
