110 
ME. W. K. PAEKEE ON THE STETTCTUEE AND 
pterygoid,” and the innermost , or submesial pterygoid, is much larger than the pterygoid, 
the counterpart of the “ internal pterygoid plate ” of Anthropotomy. In Fishes this 
bone is very constant from the Ganoid Sturgeon to the Teleostean Perch ; I have never 
seen it in the Amphibia, and as yet only in Anguis fragUis amongst the Reptilia; it has 
only failed my search in the Ostriches and Fowls amongst the Birds, and I am satisfied 
that it is not uncommon in the Mammalia. 
In the ordinary language of embryologists the mandibular arch is called the first facial, 
for the palato-pterygoid is mostly reckoned as a rudiment growing out from the man- 
dibular rod above, whilst the “ trabeculae ” had all along, until Professor Huxley showed 
their true nature, been regarded as processes growing forwards from the “ investing 
mass.” In my description of the Frog’s skull the mandibles are, on account of the 
suppressed and non-separate condition of the palatals, classified as the second facial 
arch ; in this memoir the mandibles will be considered as the third arch, but the series 
must be divided into the “ preorals ” and “ postorals.” In all Teleosteans, and in some 
to a most extreme degree, the gape of the mouth is placed at a great distance from the 
head. In such Fishes as the Dory ( Zeus ), in JEpibulus , in Fistularia , and in the “ Hip- 
pocampoids,” there is found the extreme of Teleostean modification of the mouth ; but 
in the most moderate degree of specialization, as in the Salmon, the hinge of the jaw is 
carried away from the head, first, by a double condition of the quadrate, and, secondly, 
by the descent of the top of the pier away from the side of the head and its attachment 
some distance down to the overgrown pier of the next arch (Plate VI. fig. 2, Plate VIII. 
fig. 9). All this modification shows that the Teleosteans are Vertebrates specialized to 
the uttermost for their own kind of life, and that they are indeed one of the culminating 
branches of the vertebrate Life-tree ; hence, I think, arises the wonderful harmony, in 
many respects, between their structure and that of the branches and twigs of another 
“ leader” in this genealogical tree : I refer to the Bird. 
The top of the mandibular pier, “ metapterygoid” ( mt.jpg .), is not let down so far in 
the Salmon as in the more typical Teleosteans, where it is commonly on a level, at its 
top, with the attachment of the “ stylo-hyal it passes halfway down, and both it and 
the succeeding pier being broad, it largely overlaps its successor. The whole pier is 
oblong, the upper bone, “ metapterygoid,” being squarish with produced angles, the 
lower, the “ quadrate,” triangular, with a free grooved posterior wing, and at its inverted 
apex a condyloid facet. 
Observe that the synchondrosis between these bones rises in front of the upper piece 
into a boss, and swells out behind it into a knee ; the boss is a primordial lobe ; the 
“ orbitar process ” lies in front of the eye in the long horizontal mandibular pier of the 
Tadpole (see “ Frog’s Skull,” Plate v. figs. 1 & 3, or.p.) ; the “ knee” is the retention of 
the original curve of the facial arch, which I shall afterwards describe. All in a row are 
these knees or bends in the postoral arches ; that on the trabeculae has been lost, and the 
curved part of the pterygo-palatine arch has coalesced with the orbitar process of the 
mandibular pier. On the inner side (Plate VIII. fig. 9, gu.) the quadrate is grooved, 
