142 
ME. W. K. PAEKEE ON THE STEUCTTTEE AND 
massive bars, is as yet not over large, as we see it in the adult; its long process has 
now the proper symplectic ” bony sheath (si/.), in addition to the other ectostosis on 
the main part. The opercular knob (op.c.) is large and well defined. The synchondrosis 
below the two bones is hollowed inside and behind for the head of the short “ stylo-hyal ” 
ray (st.h.), which is now enclosed in its own bony sheath. The lower end of the “ stylo- 
hyal ” is attached by a fibrous cord to the next cartilaginous bar, which has two ectosteal 
sheaths (the “ epihyal ” and “ cerato-hyal ” proper, ep.h., c.h.). The rounded cerato-hyal 
end fits into the cupped surface of the thick bulbous distal “ hypohyal” (h.li.) ; there is no 
joint cavity between them. There is a cavity, however, between the hypohyal and the 
azygous piece, the keystone of the arch ; this is the glossal hone, or true “ basihyal” ( g.h .) ; 
it has now a dentigerous bony lamina, its proper ectosteal plate, whilst the hypohyal, 
short as it is, has two centres of ossification. 
As this present paper is merely the first of a series which I hope to offer to the Royal 
Society on the Fish’s Skull, I shall refrain from making any Summary. The Teleostean 
must be studied in the light of the other ichthyic types ; there is the more need 
for this, as it is, indeed, the most specialized of all. When the “ Marsypobranchs,” 
“ Elasmobranchs,” “ Dipnoi,” and “ Ganoids” are thoroughly worked out it will be easy 
to summarize the facts obtained. With regard to the Salmon itself, the reader is 
referred to a very important work on its structure by Dr. Carl Bruch, 4 Vergleichende 
Osteologie des Rheinlachses ( Salmo solar , L.) mit besonderer Beriicksichtigung der 
Myologie, nebst einleitenden Bemerkungen iiber die skelettbildenden Gewebe der 
Wirbelthiere ’ (Mainz, 18G1). 
Description of the Plates. 
PLATE I. 
First Stage. — Embryos from the egg with simple facial arches. 
Eig. 1. Lower view of head, with facial arches shining through. x20 diameters. 
Fig. 2. Upper view of same specimen, with skin partly removed. x20 diameters. 
Fig. 3. Lower view of another head, partly dissected. X 20 diameters. 
Fig. 4. Upper view of head, undissected. X2Q diameters. 
Fig. 5. Another upper view, dissected. X 20 diameters. 
Fig. 6. Side view of head within chorion. X 20 diameters. 
Fig. 7. Another head, seen from below (dissected). X20 diameters. 
Fig. 8. Part of section of egg with contained embryo, cut longitudinally. X 20 diameters. 
Fig. 9. Head of another embryo, obliquely shown. X 20 diameters. 
Fig. 10. Transverse section, through the eyes, of an unusually symmetrical embryo. 
X2G diameters. 
Fig. 11. Another transverse section, further back. X 26 diameters. 
