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

150 F. H. Edgeworth
consist of a Dilatator laryngis, a Constrictor laryngis, and a Laryngeus
ventralis. The first-named takes origin from the fourth bronchial bar and is
inserted into the lateral process of the Cartilago laryngis; the Constrictor
laryngis consists of two half rings surrounding the Cartilago laryngis just
behind the attachment of the Dilatator; and the Laryngeus ventralis takes
origin from the lateral process of the Cartilago laryngis and passes downwards
just in front of the Constrictor and meets its fellow in a ventral
median raph6. The existence of a Laryngeus dorsalis was doubtful.
These structures are all present, as described by Gdppert, in earlier
Ichthyophis larvae, and in a late Siphonops larva. In both, however, the
existence of a Laryngeus dorsalis is certain (figs. 25, 29, 30).
In adult Siphonops the Laryngei dorsalis and ventralis have disappeared,
and the Constrictor is more developed. In adult forms of Hypogeophis and
Caecilia the Dilatator, Laryngei, and Constrictor are all present.
G6ppert also described, in a late Ichthyophis larva, a Hyo-pharyngeus
internus, taking origin from the fourth bronchial cartilage and from the
connective tissue lateral to the pharynx and passing round it to a median
aponeurosis between the pharynx and trachea and to the lateral side of the
trachea.
The muscle is present in younger Ichthyophis larvae and in larval and
adult Siphonops. In the 3-5 cm. larva of Ichthyophis the hinder part of the
muscle is overlapped by the anterior edge of the Constrictor oesophagi, and
in the Siphonops larva it is, though present, less developed-incompletely
separated from the Constrictor oesophagi and with no median raphe (fig. 31).
These phenomena suggest that the muscle is a separated portion of the
anterior edge of the Constrictor oesophagi which has gained attachments to
the fourth bronchial cartilage.
Goppert described, as one of the laryngeal muscles in a late Ichthyophis
larva, fibres springing from the dorsal fascia and inserted into that covering
the anterior part of the ventral trunk-muscles.
It is not yet developed in 3-5 and 5 9 cm. Ichthyophis larvae. In a 7 cm.
Siphonops larvae it is a slightly marked muscle lying just lateral to and behind
the fused third and fourth bronchial cartilages and tendon of Levator iv,
with no dorsal or ventral attachment (fig. 31). In the adult Siphonops it forms
a well-marked muscle arising from the dorsal fascia just behind Levator iv,
and passing downwards outside the fused third and fourth bronchial cartilages
to a median raphe just behind Transversus ventralis iv. These phenomena
suggest that the muscle in question is possibly a derivative of Levator iv.
There are, in Ichthyophis larvae and in larval and adult Siphonops, three
muscles arising in common from the dorsal fascia some distance behind
Levator iv-one passes downwards and inwards above the oesophagus, the
second passes downwards laterally to the oesophagus and is inserted into the
fascia on the medial surface of the Rectus and also to a median raphe which
is connected with the skin between the two Recti, whilst the third passes