702 
MR, T. W. BRIDGE ON THE OSTEOLOGY OF POLYODON FOLIUM. 
they evidently correspond to the symplectic ligament of the Shark. The palato- 
pterygoid cartilage is a laterally compressed bar, deep behind and concave externally, 
with a gently rounded and elevated postero-superior border and a transversely ex- 
tended articular convexity for the proximal end of the mandible. Anteriorly, in the 
orbital region, the bar becomes constricted, with its upper margin gently concave 
and its plane a little twisted, so that its outer surface looks upwards and outwards, 
and its inner downwards and inwards ; and, before curving inwards to join the corre- 
sponding bar of the opposite side, it becomes somewhat expanded, and at the same 
time tilted upwards. From the quadrate portion of the bar, a broad leaf-like out- 
growth of cartilage ( or.p .) passes forwards on the outer side of, and parallel to, the 
“ palato-quadrate ” arcade, and in close relation externally with the inner surface of the 
hinder part of the maxillary splint. To this curious outgrowth I shall have occasion to 
refer presently. The levator mandibularis muscle lies along the grooved outer surface 
of the palato-quadrate cartilage between it and the maxilla externally, and passing 
backwards from its anterior attachment curves sharply downwards behind, between 
the quadrate and its leaf-like process and passes to its connexion with the lower jaw.* 
Closely applied to nearly the whole length of the palato-quadrate lamina there is a 
thin splint-like maxilla. This bone ( mx .) has an unusual backward extension, reaching, 
in fact, as far as the condylar end of the quadrate cartilage ; its posterior third is 
closely adherent to the outer surface of the leaf-like process, and its middle third is 
separated from the main pterygoid bar by the levator mandibularis muscle, while its 
diminished and almost pointed anterior third clips the lower edge of the ectosteal 
scale (m.pg.) and the adjacent cartilage. 
Thus the maxilla in its extension backwards to the outer side of the lower end of 
the quadrate corresponds to the entire infra-temporal arcade (maxilla, jugal, and 
qua drato -jugal) of other Vertebrata, Two other ossifications have a more intimate 
relation to the “ palato-quadrate bar.” Of these, one is composed of two thin round 
scale-like exostoses applied to the inner and outer sides of the expanded anterior end 
of the bar ; each scale is marked with concentric lines of growth and separated from 
the other by intervening cartilage (fig. 8, m.pg.). The other bone is a long splint 
attached along the whole length of the inner side of the palato-quadrate cartilage 
from the inner side of the quadrate forwards to near the symphysial union of the 
two bars. Broad behind, the bone thins away in front, and its slightly sinuous anterior 
portion clips the upper edges of the two ectosteal scales. The splint is clearly 
a parosteal pterygoid, comparable to the bone so named in the Axolotl and other 
Urodele Amphibia. 
Dr. TnAQUAiRf (plate vii., fig. 2) gives an inner view of the palato-quadrate 
cartilage, showing the pterygoid ; but neither in this figure nor in fig. 1 does he 
represent the two ectosteal scales, or the leaf-like outgrowth from the quadrate. 
The proximal end of the Meckelian cartilage ( Mk.c .) is slightly bent upwards on its 
* Vide plate vii., tig. 2, in Dr. Traquair’s memoir, loc. ait. t Loe. cit. 
