OF THE MARSIPOBRANCH FISHES. 381 
fenestra, is the 1st epi-branchial; the 1st cerato-branchial is suppressed in Myxine, but 
well-developed and distinct in Bdellostoma (Plate 16, figs. 1, 2, c.br.). 
But the 1st pharyngo-branchial, or pier of the 3rd visceral arch, is well developed 
in both kinds ; here (Plate 10, figs. 1-3 ; and Plate 17, figs. 1-3, jp.br 1 .) it is free from 
its own proper descending bar, lies obliquely inside it, and is joined to the general 
thickening of cartilage in the hind part of the oval fenestra. Thence it is very thick, 
and clavatodobate, filling up nearly half of the fenestra at its inner face; it is there 
composed of hard cartilage. The rest is a soft, long, sinuous, inbent rod, which ends 
in a point some distance behind the ejpi-brancliial rays (e.br 1 .). Of the 2nd branchial 
arch only the upper or pharyngeal part is developed; but the relations of this and of 
the 1st pharyngo-branchial, enable us to determine the nature of these cartilages 
as to whether they are extra- branchials or fwfra-branchials. When the lower part of 
the throat of Myxine is removed, and the pharynx slit open for some distance 
(Plate 13, fig. 7), then we see that behind the pharyngeal opening of the posterior 
nasal canal (p.n.c.) there is a peculiar hood of membrane, the “ pharyngeal velum ” 
(vl.); it is pyriform, its narrow end is crenate, and a septum divides it behind, between 
the terminal folds. 
When this is dissected out and examined from below (Plate 15, fig. 6), then we 
find that the 1st pharyngo-branchials are the supports of its outer margin, and that 
its swelling part has a skeleton derived from the 2nd pharyngo-branchials. The 
branchial pouches and clefts, during growth, retired far away from the skeletal frame¬ 
work (Plate 9, fig. 1), so that the cleft or opening of the first or hyo-branchial pouch 
lies below the twentieth spinal nerve (sp.n .); and the middle of the pericardium is 
below the fortieth (sp.n.). All these retired parts, pushed back, so to speak, by the 
huge lingual apparatus, are supplied by a cranial nerve, the vagus—a remarkable 
“prophecy” of what will take place in the retirement of the respiratory organs in 
the higher Vertebrata. The framework of the branchial region is left in its place, and 
is largely suppressed, and the parts that are developed are free to form new specialisa¬ 
tions. The lower part of the pharyngeal velum, covered by hypoblastic cells, is sup¬ 
ported by the 2nd pharyngo-branchials (Plate 15, fig. 6, p.br 3 .), which are a pair of 
nbent, obliquely placed rods, thickish in front and very slender behind. At their 
middle they are united by a transverse bar, and this bar sends forwards two slender 
rods, which grow in front into large, pedate lobes. Where the slender hind part 
turns outwards, in the crenations of the velum, there another transverse rod is formed, 
thus uniting the right and left bars together ; this also sends off, backwards, a small 
median outgrowth, and two large, lateral, multilobate outgrowths—a curious moss-like 
structure. 
On the right side the rays of the 1st epi-branchial (Plate 10, figs. 1, 2, e.br 1 .) are 
united at their base, and form another fenestra, so that there are four visceral fenestrae 
on the left side, and five on the right. 
And yet this remarkable basket-work is not homologous with the curiously similar 
MDCCCLXXXIII. 3 D 
