ANATOMY OF BALDEN OPTER A ROSTBATA. 
229 
between the former bones and the carpus, were amphiarthrodial in character, the several 
osseous surfaces being united by a very soft, fatty fibrocartilaginous substance. This 
character of articulation also obtained between the carpals, metacarpals, and phalanges, 
without the slightest trace of synovial investments. 
Viscera. 
The mucous membrane on each side of the cavity of the mouth, which lined the 
space intervening between the lateral border of the tongue and the internal or gingival 
surface of the ramus of the lower jaw, was disposed in longitudinal folds corresponding 
to those already described as existing on the geniothoracic region of the animal. 
These folds were arranged in two sets, a superficial or primary, and a deeper or 
secondary. 
The former series were strongly marked, with deep furrows between them, and ran 
parallel to the ramus of the lower jaw. The latter, which were much shallower and 
finer, were situated in the furrows or interspaces between the former, and their course, 
instead of being parallel to the primary folds, ran in an oblique direction forwards and 
outwards across their interstices. 
This peculiar arrangement of the mucous membrane and integuments greatly facili- 
tated the expansibility of the submaxillary pouch. 
The primary folds in the immediate vicinity of the tongue were coarse and irregularly 
disposed, but as they approached the internal surface of the inferior maxilla they be- 
came smooth, fine, and more unequally scattered over the surface. 
The roof of the mouth represented in outline an elongated isosceles triangle, and 
was divided longitudinally into two smaller and more acute triangles by a prominent 
keel, formed by the inner border of the palate-plate of the superior maxillary as it over- 
lapped the vomer ; this keel extended along the central line of the palate, from the meet- 
ing of the superior maxillaries anteriorly to the isthmus faucium posteriorly. In front 
the keel was rather obscurely marked, but as it extended backwards it became much 
more prominent, and by its downward projection divided the palatine surface into two 
lateral elongated triangular spout-like concavities, each of which was deeper posteriorly 
than anteriorly, and more excavated along its inner or vomerine border, from the depth 
of the median crest in this situation, than near to its outer or labial edge, which latter 
was formed by the margin of the superior maxillary bone, where it met and was con- 
cealed by the formative nidus or Avreath of the baleen plates. The mucous membrane 
lining the roof of the mouth was dark in colour, rugose, and highly vascular. 
The free edge of the upper lips was thick and rounded, but, although they nearly 
covered the wreath, did not project downwards as far as the. level of the median palatine 
keel. The lower lips were thicker and larger. The capacity of the mouth Avas much 
diminished by the encroachment of the baleen plates, as well as by the median crest ; 
however, this seemed to be compensated for in a considerable measure by the great ex- 
pansibility of the submaxillary pouch. 
