PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
I 
descended to meet the clavicle, lyin^ over its upper border as it passed 
outwards beneath the sterno-mastoid muscle to the upper part of the 
shoulder. The third (inferior) pair were by far the largest. They ap- 
peared to be derived as a bifurcation of the great median sac at its lower 
extremity. They extended downwards among the muscles of the anterior 
wall of the chest, each branch passing out laterally under the clavicular 
portion of the deltoid and downwards under the tendon of the great 
pectoral muscle and, whilst under this, insinuating itself between the two 
portions of the small pectoral muscle (superior and inferior) into which 
that muscle divided in the animal, passing even to the axilla, and lying 
there upon the lateral wall of the chest. 
Huxley^ in his description of the Orang states that the laryngeal 
saccules attain still more enormous dimensions in the adult than in the 
Gorilla; he describes them as constituting a great median bag covered 
by a strong layer of muscular fibres from the platysma and sending 
caecal prolongations backwards beneath the trapezius muscle as far as 
the occiput, beneath the scapula and into the axilla. The cavity com- 
municated by two distinct canals with the ventricles of the larynx. 
Huxley tells us that among the Gibbons there is only one species — the 
Siamang — in which a laryngeal pouch at all similar to that found in the 
other anthropoids exists. One finds a description of laryngeal sacs in the 
Chimpanzee by Gratiolet and Alix^ in which the left pouch extended 
down between the sterno-mastoid muscles a centimetre beyond the 
upper margin of the sternum. Cunningham determined the relations 
of the laryngeal sac in a Chimpanzee and in an Orang by means of 
frozen sections. In the Chimpanzee it extended downwards in front of 
the sternum to the lower border of the manubrium ; it stretched in an 
upward direction until it reached the hollow posterior surface of the 
hyoid bone. In the Orang the laryngeal pouch, although it was pro- 
longed down to the top of the sternum, was not continued on to the 
anterior aspect of that bone. 
The occurrence of these sacs in the lower apes has been mentioned by 
Huxley, who found that among monkeys and baboons of the old world 
the sacs exist in many species ; they are not a development of the 
laryngeal ventricle in these animals, however, but grow out from the 
thyro-hyoid membrane, and have only a single aperture of communi- 
1 Loc. cit., Vol. I, p. 596. 
2 Gratiolet and AHx, “ Recherches sur I’Anatomie du Troglodytes Aubryi,” Nouvelles .archives du 
Museum d’Histoire Naturelle, Paris, Vol. II, 1866, p. 232. 
3 D. J. Cunningham, “ The Topographical Anatomy of the Chimpanzee, Orang-utan and Gibbon,” 
Cunningham Memoirs, Royal Irish Academy, 1886, p. 138. 
