12 
PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
cation with the laryngeal cavity. In the apes of the new world some 
extraordinary variations occur in the development of these air sacs. In 
the spider monkey (Ateles) Huxley describes a single median sac which 
is developed at the back of the trachea, opening into the air passages 
between the upper ring and the cricoid cartilage. Then, again, in the 
howling monkey (Mycetes), according to the same authority, the hyoid 
and the laryngeal apparatus is exceedingly developed and modified. 
“ The body of the hyoid bone is expanded into a great rounded drum 
with thin osseous walls, the larger cornua projecting backwards from it, 
though the lesser pair are quite obsolete. The thyroid cartilage is also 
exceedingly large, and the epiglottis undergoes an extraordinary 
development and changes in form. The cavity of the glottis presents 
several prolongations ; one long and narrow tube in front communicates 
with the chamber in the body of the hyoid bone, the two lateral sacculi 
are prolonged upwards on each side, and are only separated from each 
other above the larynx by a thin membranous septum, and in some 
species there is, in addition, a small inferior pair of sacs.” ^ The howling 
monkey, as its name implies, is capable of uttering loud and discordant 
sounds, and no doubt the complicated apparatus just described has 
something to do with the production of these sounds. It is difficult to 
understand how the mechanism acts, and I am not aware that anyone 
has succeeded in solving the problem. 
I have thus given an account of the laryngeal sacs as they are 
found in the anthropoid apes and in apes lower in the scale. They are 
undoubtedly developed in connection with the laryngeal ventricles^ 
structures which are present in the human larynx. These ventricles — 
the “ ventricles of Morgagni ” — lie in the lateral walls of the larynx, one 
on each side. The ventricle may be described as a recess which exists 
between the false cords above and the true cords below; it there forms a 
diverticulum from the lateral wall of the larynx, presenting an elliptical 
opening, the length of which is a little shorter than the true cords. The 
ventricle is about 5 mm. in depth, and, in man, from the anterior part a 
secondary diverticulum proceeds, the so-called “ laryngeal pouch” which 
extends upwards for about 12 mm. towards the upper border of the 
thyroid cartilage ; it is apparently this laryngeal pouch which assumes 
such enormous proportions in the Orang. According to Testut^ this 
pouch is sometimes found considerably enlarged in man ; whilst it 
usually terminates at the upper border of the thyroid cartilage, it may 
proceed upwards as high as the hyoid bone, or even sufficiently high to 
appear under the mucous membrane of the base of the tongue. 
I Loc. cit. Vol. II, p. 123. 
a L. Testut. “ Traits d’Anatomie humaine,” Troisieme Edition, Paris, 1895, Vol. Ill, p. 359. 
