98 
MR. W. K. PARKER ON THE STRUCTURE AND 
his excellent paper on the Polypterus (‘Journal of Anatomy and Physiology,’ vol. v.) ; it 
has helped me greatly, beautifully showing the meaning of the earlier “ Ganoid ” stage 
of the Salmon’s skull. 
Structure of the Adult Salmon's Skull. — Eighth Stage. 
I begin with the adult, and this because of the multiplicity of parts in the Teleostean 
skull : he has mastered no easy piece of work who knows these parts and their relations. 
On the upper surface of the Salmon’s skull there are five important parastoses — namely, 
the “ superethmoidal,” the frontals, and the parietals (Plate VII. fig. 1, eth., f., p.). 
The parietals (p.) are small, ridged, subarcuate bones, separated by the whole width 
of the broad supraoccipital (s.o.) ; they articulate with it, and also with the corresponding 
frontal (f.) and with the epiotic {ep.); their relation to the ossified and unossified skull 
proper is shown in section (Plate VIII. fig. G, p., s.o.). 
The frontals (_/*.) are, as is usual in the Teleostei, very large; they only meet to form 
the sagittal suture in their hinder half, for further forwards the smooth strong ridge of 
the cartilaginous skull separates them. They rise thin towards the edge, and at the 
base of this ascending lamina there is a considerable sulcus, outside of which they expand 
to an equal size again in front, and to twice the width behind. The fore and outer part 
is leafy and jagged, so is the hinder half at its extreme width, in its supraorbital portion ; 
but the rest is a thick bed of excavations for fatty tissue. The exact relation of the 
frontals to the skull proper is shown in a series of transverse sections (Plate VII. figs. 
8-11, and Plate VIII. figs. 4 & 5,/.). 
The character of the frontal roofing is well shown by the effect produced and the 
parts exposed when these bones are removed (compare Plate VII. fig. 1 with Plate VIII. 
fig. 1). 
The fore part of the cartilaginous skull is covered in by a bone (Plate VII. fig. l,e< th.) 
which has been the subject of much discussion; and here the Salmon shows itself to be 
a halfway type between the typical Teleostei and the Ganoids. 
In the “ Siluroids,” for instance Callichthys and Clarias (see for the latter, Huxley, 
Mem. of Geol. Surv. decade 10th, 1861, p. 30, fig. 20, eth.), there is a large Ganoid scale 
in this region, similar to what is found in Coccosteus {op. cit. p. 30, fig. 19, eth.). Now 
in the “ Siluroids” the dermal scute has coalesced with a true meso-ethmoidal bone, 
formed by an ectostosis ; but in the Salmon that region of the skull is entirely unossified, 
and the bony plate is parosteal. In another malacopterous fish, the Pike {Esox lucius), 
there are two ossifications in the meso-ethmoidal cartilage, one on each side in front 
(see Huxley, ‘ Elem.’ p. 186, figs. 7. 3, A, B, C 3), and the long, flat snout is overlain 
by a pair of parostoses {op. cit. p. 168, fig. 69. 2). Then in other Malacopteri, namely, 
the “ Cyprinoids,” there is a proper median ossification of the meso-ethmoidal cartilage 
(see Huxley, Croon. Lect. p. 24, fig. 6, eth.) ; and this is the state of things in the 
“ Acanthopteri” (e. g. Zeus ) and the “Anacanthini (e. g. Gadus). In the “Ganoid” 
Polypterus , the median, proper meso-ethmoidal bone is invested by a pair of large ganoid 
