128 
ME. W. K. PAEKEE ON THE STEUCTUEE AND 
it, like the arms of a swimmer, have already coalesced, and send their outspread palms 
beneath the nasal sacs, to which they form a floor, as well as serving in this complex 
building the purpose of beams to the brain-chamber and rafters to the palate*. 
Nothing, perhaps, in the whole Vertebrate morphology has such a vegetative freedom 
of growth into branch-like and leafy outgrowths, spreading outwards and reaching far 
fonvards, as the first facial arch. Yet it is upon the trabecular modifications that the 
very facies of the types largely depends ; the Shark, the Sawfish, the Skate, the Tortoise 
and the Bird, the Whale, and even Man himself, all these largely owe their “ progna- 
thism ” or their “orthognathism” to arrest or extension of the trabecular growths. 
Here, as in the Polypterus (Traquair, op. cit. plate 6. figs. 2 & 3), the muzzle is broad 
and depressed, owing to the great outgrowth of the early two-leaved end of each trabe- 
cula. Upon the coalesced “ cornua” (Plate IV. fig. 2) there has arisen an elegant 
X-shaped rudiment of the median ethmoid and nasal septum in one. Between the 
hinder legs of the X is seen an opening (shown also from behind in Plate III. fig. 7); 
this deficient fusion of the two sides thus preserves the counterpart of the Lamprey’s 
nasal opening (Muller, op. cit. plate 4). On each side of the median upgroAvth we 
see the “ subnasal lamina” (figs. 1-3, s.n.l.), on each side of the snout the divided 
“ upper labials,” and outside the ethmoid the articulation of the palato-pterygoids (ppg.)- 
The X-shaped “ mesoethmoid” (ossified in Polypterus, see Traquair, figs. 1-3, P) is 
continuous with the shelving, inturned “ ectoethmoid” (Plate III. figs. 7 & 8, l.e. 1); 
these growths, hard to be understood, are continuous below with the pedicle for the 
palatal facet (Plate IV. figs. 1-3, and Plate III. fig. 7). Where the olfactory crura 
escape in front to ramify on the nasal sacs (Plate III. fig. 8, i), there the ectoethmoid 
can be seen to be continuous, below, with the outspread “ trabecular cornua” (“ sub- 
nasal laminae”), and above to have a mutual bond in the new cranial roof over the 
“ prosencephalon ” (C l 4 ). In the transverse section through the nasal sacs (Plate III. 
fig. 7, ol.) the commencement of the sloping roof is, of necessity, cut through obliquely; 
but its structure and meaning cannot be misunderstood if it be looked at in the dis- 
sected and bisected skull (Plate IV. figs. 1-4). This elegant roof has no side walls to 
support it ; it is, as it were, thrown like a tarpaulin over the brain-sac (see also Plate 
III. fig. 9), and is tied by cartilaginous ropes, behind, to the Avails of the ear-chamber. 
Where this structure is cut through at its convergence in front (Plate III. fig. 8) we 
have a cincture of cartilage (see Dr. Traquair’s remarks, op. cit. pp. 170, 171), similar to 
that which is seen in the Frog (“Frog’s Skull,” Plate vn. fig. 9). 
This ethmoidal “ tentorium” contracts and thickens to form the part which in the adult 
* We must be very cautious of interpreting continuity of even cartilaginous structure as necessarily indicating 
morphological simplicity. Here, in the Salmon, the cranium is free from the trabeculae as it is not in other 
types. We must keep also an expectant watch for the solution which may turn up of the after division of 
the skull-segments and ear-organs of the Mammalia ; in that class there seems to he a reversion to even a 
Myxinoid type of structure, for the nasal sacs, growing backwards under the skull, divide the trabecular base 
from the proper cranial floor. 
