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

156 F. H. Edgeworth
The development of the pars trachealis cartilaginis lateralis is related to
the formation of a trachea which develops at the end of the larval stage in
Rana, during larval life in Menopoma, Amblystoma, Triton, Siphonops
and Ichthyophis, and in the 20 mm. stage of Necturus. The pars trachealis
is formed as a non-chondrified backward prolongation of the pars laryngea
s. arytenoid. It may persist in this condition, e.g. Necturus, or may subsequently
chondrify in tracts of more or less complete rings. In Triton and
Salamandra the cartilage is first developed at the bifurcation of the trachea.
The above discussion shows that further embryological investigations are
needed-in particular it would be well to know the condition of the bronchial
skeleton and ventral bronchial muscles in the larvae of Amphiumal and
Cryptobranchus jap., the development of the sphincter laryngeal fibres in
Siren, and the development of the ventral bronchial muscles, larynx and
laryngeal muscles in Gymnophiona.
On the phylogenetic history of the larynx, trachea, and laryngeal muscles
Schmidt (1913), who investigated the development of the larynx in
certain Reptiles, was of opinion that the lungs of Polypterus, Amphibia, and
Amniota, like the swimming bladder of Lepidosteus and Amia, develop in the
same native soil ("Mutterboden"), and that, on the other hand, the trachea
with the larynx of Amniota, and possibly also that of Amphibia, are phylogenetically
a later formation, the development of which begins with pulmonary
respiration.
The larynx of Dipnoi and Polypterus lies in the ventral wall of the gut
behind the bronchial region. Its musculature was described by Wiedersheim
(1904) and Gbppert (1904). They came to the conclusion, though without any
embryological evidence, that it is developed from pharyngeal musculature
and that it represents musculature of atrophied bronchial arches.
Neumeyer (1904) and Kellicott (1905), independently, showed that the
larynx of Ceratodus is developed in the ventral wall of the gut at some distance
behind the bronchial region. Greil (1913) confirmed their observations, and
also showed that the free mesoderm cells round the gut and larynx become
spindle-shaped and develop into smooth muscle cells, which form a mantle
round the gut and larynx.
Kerr (1910) stated that in Lepidosiren and Protopterus the lung-rudiment
is developed, in stage 32, as a mid-ventral bulging from the pharynx at the
level of cleft vi. His figures show that its connection with the gut migrates
backwards, so that in stage 35 it is distinctly posterior to the level of the
6th gill-clefts, i.e. is in the oesophageal region. In Lepidosiren, Agar (1907)
stated that the ventral and lateral parts of the "Constrictor pharyngis" of
Wiedersheim are formed from mesenchymatous cells, budded off from the
inner walls of the pericardio-peritoneal ducts, and are thus of splanchnic
origin. The dorsal part of the muscle is of somatic origin, being derived
I In larvae younger than the 45 mm. stage investigated by Hay.