418 HARRIS HAWTHORNE WILDER ON 
seen the internasal plate of the primordial skull. Viewed from the ventral side, the two 
vomers may be said to overlap the parabasal, and the areas of contact are clearly marked 
upon the dorsal surface of the former bone and the ventral surface of the latter. The 
frontal bone comes in contact with the vomers dorsally, and the articular surface for this 
forms a long, narrow ridge, running along the lateral border above the row of teeth. At 
the extreme anterior end, the two vomers come in contact with each other, the symphysis 
being marked by a few jagged, irregular projections. The postero-lateral border of the 
palatine portion is recurved and exhibits an articular surface for the anterior end of the 
palato-pterygoid. 
b. Palato-pterygoid. — This is a flattened bone, somewhat in the form of a narrow 
parallelogram, but with the anterior end rounded. It is set in the skull obliquely to the 
longitudinal axis and extends from the vomer to the quadrate, articulating with both and 
with no other bones. Its alveolar portion is small and confined to a short curved ridge 
upon the outer border at the anterior end. The space 
ay between the inner border of this bone and the outer border 
of the parabasal is in the form of a very narrow triangle 
and is filled in the recent state by a firm membrane. The 
Alveolat pottion 
orientation of this bone may be easily made by the teeth 
which are upon the ventral side, at the anterior end, and 
along the outer margin. 
The Visceral Skeleton. 
AL TRAL . . 
Pee eas General morphology of the arches.— The seven visceral 
Fige15." Two views of right pal: arches inherited from the Selachians, and surviving in most 
ato-pterygoideum. X 4, (from small f 
higher vertebrates, are represented here, although one of 
specimen). Contact surfaces with 
other bones are designated by an x. them (the 6th) is vestigial, and appears in the adult as 
merely an intermuscular septum. Their disposition is as 
follows : — 
1. This arch, forming the functional jaws of the Selachians, possesses typically 
a dorsal and a ventral segment, of which the former is represented by the cartilaginous 
palato-quadrate arch, and the latter by Meckel’s cartilage of the mandible. Both of these 
arches, in most higher vertebrates, become encased by dermal bones and lose their 
identity more or less completely in the adult, the palato-quadrate arch suffering more 
in this particular than the other. In Necturus the anterior and posterior ends of the 
palato-quadrate arch survive as the antorbital process and the quadrate cartilage 
(including its ossification) respectively, and the median portion is unrepresented. The 
