384 
MR, W. K. PARKER ON THE SKELETON 
5 
backwards, and inwards, and they are shaped like a lancet blade, but with a slight 
curve, the convexity being a.ntero-internal. A cavity can be seen in them, and also 
that they are made of fibres arranged featherwise. The thick horny layer is 
continuous at the base of the teeth ; their form is due to the folding of the lining 
membrane of the mouth, which undergoes corneous hypertrophy of the cells. These 
structures will be described again, when we come to the sections. The only antagonist 
tooth is very large and canine-shaped, attached to the ethmoid below, and pointing 
backwards (Plate 10, fig. 3, et.t.) ; an arrangement similar to that in “ Cyprynoids,” 
where the basi-occipital, horny tooth antagonises the lower pharyngeal, true teeth. 
On the branchial pouches of Myxine. 
The extraordinary displacement of the branchial pouches in the Myxinoids is 
correlated with, or even caused by the enormous size of the lingual apparatus, the 
fore part of the great common basi-branchial bar being retained with the basi-hyal 
at the hind part of the lingual skeleton (Plate 9, figs. 1-3). But even this only 
reaches half way along the base of the oblique muscles that work the tongue. There 
is, however, a second basi branchial bar (fig. 4, h.br 2 .), slenderer and flatter by far, and 
only half the length of the main part ; this is composed of hard cartilage, and after 
a space equal to its own length finishes the skeleton of the apparatus along the basal 
line. 
In Myxine there is no skeleton to the six pairs* of cake-shaped ( placentiform ) 
branchial pouches, but the whole structure is membranous (see J. Muller, I., plate 7, 
figs. 10-12 ; and my figure Plate 9, fig. 1). 
Each pouch opens inwards into the narrow pharynx by a wide passage, and out¬ 
wards by a largish tube which communicates with the opening of each succeeding 
tube, until they all have a common escape opening, behind. Into this space, on the 
left side, there is a sort of fistulous passage —the “ ductus cesophago-cutaneus ” (d.ce.c.) 
behind the last pouch—a sort of abortive gill-cleft, with no gill structure, the use of 
which I cannot see, but the morphology of which is self-evident. Behind these is 
the large heart ( h .), giving off the arterial arches to the gill pouches.t 
On the sense-capsules of Myxine. 
For a detailed account of these organs, the reader is referred to Muller’s Memoirs; 
and for the auditory organs, especially, to Professor Retzius’s magnificent volume, 
just published.| 
* Mr. Weldon informs me that he has found some specimens of Myxine glutinosa with seven pairs of 
pouches. 
f For details see J. Muller, I., plate 7. 
X ‘Das Gehororgan der Wirbelthiere,’ vol. i., plates 1, 2, pp. 3-12. Stockholm: 1881. 
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