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ME. W. K. PARKER OK THE STRUCTURE AND 
have to be compared with such facial growths as may exist in front of the mouth, 
and these, if possible, have their relation to the post-cephalic arches determined. 
Long ago, to those who knew nothing of Embryology, all this seemed to be easy 
enough ; now, with all the new, increased light from that source, the problem has 
become extremely difficult, and is certainly not solved, as yet. 
I do not see that the superficial cartilages that surround the mouth have any right 
to be compared, serially, to the arches of the pharynx or of the chest; they appear to 
me to be the most archaic structures in the skeleton—*“ barbels,” “labial cartilages,” 
“nasal valves”—all these appear to me to be lineally descended from the inner 
supporting tracts of tissue of oral palpi, such as are met with in so many of the 
aquatic hwertcbrata. The investing bones of the face may be grafted on such 
cartilages, but the two things are quite different in their nature. The condition of the 
visceral arches in this type, both in the larva and in the adult, has led me to 
reconsider the whole question of the nature of these arches. 
There are several things to be considered at the outset, before a comparison is made 
of the skeleton of the throat, the branchial skeleton, and the skeleton of the chest. 
The post-auditory part of the cranium has manifestly undergone secular shortening, 
so that the pharyngeal or ventral region belonging to it often extends under the twice- 
segmented spine, whose fore part is, so to speak, intercalary or superadded, and does not 
correspond with the arches beneath it, which often extend backwards for some distance. 
At one time this appeared to me to be an explanation of the fact that the inner 
(or proper) branchial arches of Fishes are developed beneath the fore part of the spine 
and the hind part of the basis cranii, whilst the mandibular and hyoid arches, the first 
and second of the branchial category, often fix themselves to the basal plates of the 
cranium. 
I now strongly suspect this view of the matter to have been a mistaken one; and 
that it is the abnormal size and special modification of the mandibular and hyoid 
arches that make it necessary for those arches to seize hold of swinging points above 
their normal dorsal region or apex. 
I think that the figures I have given of the visceral arches in the larval Sterlet 
(Plate 13, figs, 6 and 11) will make my meaning plain. Here only one arch is 
attached to the edge of so much of the parachordal plate as may creep under the 
auditory capsule; all the other arches are fairly under the head and forepart of the 
neck. 
This normally inferior position of the visceral arches is best seen however in the 
early embryo of the Skate (see in “ Pristiurus,” Trans. Zool. Soc., vol. x., plate 35, 
fig. 4), where the metapterygoid, hyomandibular, and all the pharyngo-branchials, are 
shown in situ , after the whole cranium had been removed from above. 
The sub-division of the pleuro-peritoneal cavity by the hypoblastic branchial pouches 
in the early embryo, the rapid closure of those cavities (the “head-cavities”), and the 
relation of the skeletal bars of the pharynx and mouth, whether deep or superficial—all 
