574 
cally; no animal on the other hand, possesses both. The fibro-carti- 
laginous developements surrounding the Rima glottidis in Dipnoi and 
in some Ganoids are not homologues of the Arytaenoids, but arise in- 
dependently on account of the same necessity. This has been univer- 
sally admitted previously. 
b) The sudden appearance of such well-developed hyaline struc- 
tures as they appear from the first, as well as the sudden disappear- 
ance of other well-developed structures (the 5th branchial arches) 
are both unusual phenomena, and when considered together, may well 
point to the above theory. 
c) In the Selachian the 1st of the branchial arches is supplied by 
the glosso-pharyngeal nerve, while the other four are under 
the control of four primitive Vagus elements, the 5th arch thus 
being supplied by the 4th (X, in the diagram, fig. 2). This same 
\ 
i \ 
N 
¥ i ; : i 
Br. es (Bea tales ciel iy Ma 
Fig. 2. Diagram of early condition of visceral arches and super- 
ficial muscles. Md. Mandible. Hy. Hyoid. Br. 1—5 Branchial arches. V. Trige- 
minus. VII. Facialis. IX. Glosso-pharyngeus. X1—4 The four Vagus elements. 
nerve follows the Arytaenoids and supplies this region throughout the 
Vertebrate realm, under the names of Ramus recurrens, Recurrent 
laryngeal, Inferior laryngeal etc. 
d) Another example of former branchial arches entering the 
service of the larynx is furnished by the thyroid cartilage, which 
developes later from the 2nd and 3rd branchial arches (pu Bots). 
2. The tracheal elements are to be considered new 
structures, and arise directly from the connective tissue 
immediately surrounding the tracheal mucous mem- 
brane, through thenecessity of keeping the air passages 
