1045 
Chimpanzee or the Gorilla, but are developed to a large air-cushion 
which, embracing the neck, extends far over the breast and the 
shoulders, and on which the head rests in front and on the sides '). 
Deniker and BovrarT, and also Heck are inclined to consider the 
large laryngeal sacs of the Orang-utan as support for lower jaw 
and parts of the head, the muscles of the neck being much less strong 
than in the other large Anthropoids*). Probably not in contrast with 
the much smaller laryngeal sacs of the other Anthropoids mentioned, 
their functional meaning is certainly not connected with the voice, 
for the Orang-utan is almost dumb. Nor is their large size in the 
Orang-utan in connection with an extra-ordinary weight of the 
head; that of many Chimpanzees is no less heavy, and the head of 
the Gorilla is certainly generally heavier. The laryngeal sacs of the 
Orang-utan grow with the general growth of the animal, and are 
larger in males than in females, largest in gigantic old males. As 
the head gets heavier, the laryngeal sacs increase in volume. They 
support the head also on the side, and it seems that they can be 
assisted in this by the cheek lobes, for where these occur, the 
laryngeal sacs are comparatively less large *). 
But in Anthropoids and other Apes, in contrast with what happens 
in Homo sapiens, the head is not carried poised on the vertebral 
column, but in most it is carried strongly hanging over; the centre 
of gravity then lies far before the supporting line of the condyles, 
and very powerful muscles of the neck carry this overhanging 
weight. The muscles of the neck in the Orang-utan are directed 
much less steeply with regard to the “horizontal planes” of the skull, 
consequently the planum nuchale is steeper than in the other 
Anthropoids, for instance in the Chimpanzee. The angle of the 
basio-nasal line with the basio-inion line is about 30° smaller in the 
Orang-utan, and the angle of the plane through the middle of the 
condyles and the nasion with the condylo-inion-plane 22° smaller 
than in the Chimpanzee. This means that only with an elevation of 
the head of the Orang-utan of 22°, when in front it certainly rests 
1) R. Fick (Vergleichend anatomische Studien an einem erwachsenen Orang- 
Utang. Archiv fiir Anatomie und Entwickelungsgeschichte. (W. His), Jahrgang 
1895, p. 75) found at the dead body that when the laryngeal sacs are swollen, 
the head was greatly lifted up backward, without his seeing in this an indication 
of the vainly sought functional meaning of that air sac. 
9) Deniker and Bovutart in Nouvelles Archives du Muséum d'histoire naturelle, 
Paris 1895. sér. 3, t. VII, p. 47—48. Breums Tierleben. Vierte Auflage. Säugetiere, 
Bd. IV, Primates. Bearbeitet von L. Heck, p. 630. Leipzig. 1916. 
5) Cf.: C. Kerpert, Reuzen-Orangoetans, in „Natuur- en Wetenschap”. Eerste 
Jaargang, p. 7. Brugge 1914. 
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Proceedings Royal Acad. Amsterdam. Vol. XXIII. 
