on the development of the hypobranchial and laryngeal muscles in ...

142 P. H. Edgeworth
Ellipsoglossa. My observations show that it is also present in the larval stages
of Ellipsoglossa and Menopoma.
It is a muscle that takes origin from the fourth bronchial bar, passes
forward and separates into three slips (a, b, c) which are attached respectively
to the first, second and third bronchial bars. In Siren only (a) is present.
In Necturus and Proteus there is a similar Subarcualis rectus iii which takes
origin from the third bronchial bar, and is attached, (a) to the first, and (b)
to the second, bronchial bar.
The forward extension of Subarcualis rectus iv in front of the third
bronchial bar-to the second and first bars-is related to the secondary
function and position of Subarcuales ii and iii. (It is noticeable that this
secondary form of Subarcualis rectus iv also exists in Amphiuma (adult), and
that in Megalobatrachus max. (adult, with only two bronchial bars) though no
Subarcualis rectus iv is present yet Subarcuales obliqui ii and iii and not
Subarcuales recti ii and iii are present videe Druner). These facts form
additional evidence in favour of the theory, suggested above, that a Urobranchiale
exists in the larval forms of these Urodela also.)
There are thus five closely related phenomena in Urodela. (1) Backward
growth of the hind end of the Genio-hyoid ventral to the forepart of the
Rectus cervicis. (2) Formation of a Urobranchiale. (3) Formation of Subarcuales
obliqui ii and iii (Subarcualis obliquus ii in Necturus and Proteus).
(4) Forward extension of Subarcualis rectus iv (Subarcualis rectus iii in Necturus
and Proteus) to the first branchial bar. (5) Separation of a superficial,
ventral, portion of the Rectus cervicis, attached to the Urobranchiale.
No one of these secondary phenomena occur in Anuran and Gymnophionan
larvae, where the conditions are more primitive. (There is a small overlap
of the Genio-hyoid and Rectus cervicis in Rana temp. larvae, but it is due to
a backward extension of the former along the hypobranchial plate, and so of
a different character from that of Urodela. The anterior end of the Rectus
becomes attached to the Crista hyoidea (of Schultze), but this, as shown by
Gaupp, is a ventral process of Basibranchiale i, and so not homologous with
the Urobranchiale of Urodela.)
Transversi ventrales. Transversus ventralis i is present in larvae of Ichthyophis
and Siphonops, but not in Anuran or Urodelan larvae. Transversus
ventralis ii is not found in any Amphibia. Transversus ventralis iii is present
in Necturus, and probably in Proteus, but not in other Amphibia. Transversus
ventralis iv is present in larvae of Anura, Gymnophiona, and Urodela with
four bronchial bars. In Rana the muscle is rudimentary and soon disappears.
In Ichthyophis it is attached to the fourth bronchial bar, and, on the fusion
of this with the third, to the fused bar, by two heads in Ichthyophis, by one
in Siphonops.
In Menopoma, at the stage when the sixth gill-cleft reaches the ectoderm,
the ventral end of the fourth bronchial muscle-plate (attached to the pericardial
wall) and the primordium of the fourth bronchial bar are in front of