513 
portions of the cartilages being left in their original lateral position 
as posteriorly extended processes. In the same animals the Ary- 
taenoids are highly developed, forming a sort of hollow resonance box 
for the vocal chords. In some the extreme anterior apex separates 
from the remainder of the cartilage, and is movably articulated 
with it, the so called cartilage of SANTORINI. 
In the Aglossa, Pipa and Dactylethra, the hyoid apparatus 
forms an enormous box to enclose the larynx. Inside this box lie 
the laryngeal cartilages, the Arytaenoids being so small as to have 
been entirely overlooked by HENLE, who consequently gave the wrong 
determination to the other parts. These, rather numerous, are the tra- 
cheal elements, the upper pieces being recognized by comparison with 
other Anourans as portions of the usually fused mass; while poste- 
riorly the elongated bronchi necessitate the developement of pieces 
similar to tracheal rings. 
In the Caecilia, the tracheal elements attain a high developement, 
separating into several pieces and forming more or less regular tra- 
cheal rings as in higher animals. The Arytaenoids are here still in 
a very simple condition. 
c) Origin of the respiratory cartilages. 
It has already been stated that the Arytaenoid cartilages differ 
in age of developement from the tracheal elements, thus sug- 
gesting the possibility of their differing also in origin. 
I am quite persuaded that a most important morphological fact 
has here been emphasized, and have carried out this ideain the follow- 
ing conclusions. With the consciousness that my investigations have 
as yet been insufficient for positive assertions, I submit the following 
as working theories, the refutation or substantiation of which, either 
by myself or others, I shall await with interest. 
1. The arytaenoid cartilages are no new forma- 
tions, but are the missing 5th branchial arches, present 
and gill bearing in the Selachians, and forming in Te- 
leostei the so called inferior pharyngeal bones. 
They are thus phylogenetically the oldest of all 
the laryngo-tracheal cartilages, and appear as such at 
the moment when the growing importance of the lungs 
renders the distension and regulation of the air-pas- 
sages a necessity. 
This theory appear to be supported by the following facts. 
a) Every animal possesses either a 5th pair of branchial arches, 
or a pair of Arytaenoids, in the same location, topographi- 
