distended. In their simplest form they appear as a single pair 
(Triton), sometimes, however, being very long and extending a 
double series of teeth towards the middle line (Siren, Amphiuma). 
In higher Anourans they often unite across the median line and 
form a ring, the so-called “‘Cricoid”, while in others (Dactylethra 
and the Coecilia) several tracheal rings are formed. From this we 
may conclude, however, that the “ericoid”, formed by the fusion of 
the tracheal elements, is not the homologue of the mammalian Cricoid, 
since there it represents only one, or at most a few, of the upper 
tracheal rings, while here all the tracheal elements enter into 
its composition. That the above is the true origin of the tracheal 
elements I have assured myself both by a study of the lower Uro- 
deles and of the embryonic condition in higher forms. 
In Siren and Menopoma they are composed of a sort of 
fibro-cartilage, not well differentiated from the surrounding connective 
tissue, while the Arytaenoids are clearly defined, hyaline masses, 
movably articulated with the former; the prolonged posterior processes 
of the Arytaenoids being, as it were, partly imbedded in the fibro- 
cartilaginous tracheal structures. In embryo Tritons the develo- 
pement of the tracheal elements from the connective 
tissue of the tracheal walls can be distinctly seen, at 
a time when the hyaline Arytaenoids are already well 
developed. 
2. Muscles of the larynx. 
a) The general type. 
This subject may be best understood by a study of the accom- 
panying diagram, fig. 1. The figure is almost identical with the adult 
condition of the lower Urodeles; but all Amphibian forms, even those 
of the most aberrant Anourans, may be easily reduced to it. It will 
be noticed that the muscles of the larynx divide themselves into two 
systems, an intrinsic system, consisting of a ring placed around the 
glottis, and an extrinsic system of laterally placed transverse bands, 
very inconstant in origin, insertion, and position. These two systems 
with their derivatives will be taken up in order: 
b) The intrinsic system (the muscular ring). 
As typical form may be taken Siren or Menopoma, where 
the larynx is surrounded by a complete ring. The Arytaenoids are 
partly enclosed by this ring, and partly lie in its substance at the 
sides, serving to more or less completely divide the ring into a dorsal 
and ventral half. In all except the lowest forms, this division is com- 
38 
