OF THE MARSIPOBRANCH FISHES. 
405 
The Myxinoids come near to the adult Lamprey in the following particulars, 
namely :— 
a. There are developed outside the skull proper, but not segmented from it, palato- 
quadrate and hyoidean cartilages. 
b. There is a very large median cartilage belonging to both the hyoid and branchial 
regions. 
c. The cranium acquires a floor by the development of a special hinder inter¬ 
trabecula. 
d. There is a large median cartilaginous olfactory capsule. 
The Myxinoids go beyond even the adult Lamprey in the following characters, 
namely:— 
a. The facial basket-work is much more perfect, and as this is a generalised 
condition of the true intra-visceral system of cartilages, it is a very important 
character. There is not only an equal development of the “ suspensorium,” but the 
suspensorial part of the hyoid is developed also (it is suppressed in the Lamprey); 
and there is (in Bdellostoma) a large complete 1 st branchial arch, and in both kinds 
pharyngo-branchial rudiments of the 2nd branchial arch. 
b. The respiratory pouches are much more specialised, being carried far back under 
the spine. 
c. There is not only a very distinct sub-cranial intertrabecula, but also a large pre- 
cranial or nasal median cartilage of the same nature. 
d. The opening to the median olfactory sac is not a mere short membranous passage, 
but a long tube, encased in a series of cartilaginous (imperfect) rings. 
e. Correlated with the non-deve 1 opment of the suctorial labia) apparatus, there is 
an enormous development of the lingual, this basal bar becoming not only double, but 
in front quadruple ; and the “ supra-lingual cartilages,” which are very small in the 
adult Lamprey, and carry only one pair of rows of small recurved teeth, in the Myxinoids 
are very laige, and carry two pairs of rows of large teeth, with the addition of a 
median ethmoidal antagonist tooth. 
Lastly, the greater development of the intra-visceral cartilages is correlated with 
the suppression of the extra-visceral basket-work, seen both in the larval and adult 
I Lamprey, and also in the larvse of the “ An lira,” generally. 
i 
3 G 
MDCCCLXXXIJI. 
