PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
25 
Bischoff^ also remarks upon the fact that the intermediate tendon 
often fails to develop in the ape; in Bischofifs Oran^, however, the whole 
muscle failed. This authority also refers to an Orang dissected by Alix 
in which the omo-hyoid arose from the clavicle as well as from the 
scapula ; this variation in the Orang is of interest, because a similar 
variation sometimes occurs in man. The total absence of the omo- 
hyoid is not rare in man; of this Testut^ has recorded nine cases. Again 
the absence of either the anterior or posterior belly may occur, and the 
bony attachment more particularly of its posterior belly is subject to great 
variation in man. Gegenbaur,^ after a critical study of the varieties 
of the omo-hyoid as it occurs in man, and the conditions of its develop- 
ment met with in the lower animals, concludes that it belongs to a 
muscle group including in man the sterno-hyoid and sterno-thyroid 
muscles. These muscles in some animals (reptiles) form a continuous 
attachment from the sternum, along the clavicle to the scapula. 
Referring the omo-hyoid to such a group of muscles we can readily 
explain the occurrence of the intermediate tendon and the variation in 
the bony attachments, sometimes to the clavicle, sometimes to the 
scapula, or it may be to both bones. 
The Sterno-inastoid had an extensive origin from the mastoid process 
and the occipital bone, and was inserted by two heads, one into the 
manubrium sterni on its anterior aspect, and the other into the inner 
fourth of the clavicle. Cuvier^ figures the sterno-mastoid in the Orang 
as two very distinct muscles, the clavicular portion arising from the 
skull below the sternal portion and proceeding to its insertion into the 
clavicle. In the Gorilla it is usually in two distinct portions, as indeed 
it is also in the other anthropoids. The two portions of the sterno- 
mastoid in man are separated from one another by a varying interval 
at their insertion. 
The Pectoralis major ^ consisted of three very distinct portions : — (i) 
Pars costo-abdominalis (plate IV, fig. 2, p.m. /), which arose from the 
osseous part of the fifth rib near its sternal extremity, and by an origin 
4 cm. wide from the aponeurosis of the external oblique muscle of 
the abdomen. l‘he fibres passed very obliquely upwards and outwards 
and lay on a plane posterior to the other two portions of the muscle. 
The insertion was into the strong fascia over the biceps tendon, and 
1 Loc. cit., I, p. 205. 
2 Loc. cit., Vol. I, Pt, 2, p, 677. 
3 C. Gegenbaur, “ Ueber den Musculus Omohyoideus und seine Schlusselbelnverbindung.” Morpholo- 
gisches Jahrbuch, Vol. I, 1876, p. 264. 
4 Loc. cit., plate 15. 
