1898-99. | THE ANATOMY OF THE ORANG OUTANG. 567 
in the leg as the homologue of the'pronator radii teres in the forearm, 
The occasional second head of origin of the muscle from the fibula in 
man may correspond to the ulnar origin of the pronator. Bischoff’ 
admits that pronation is possible to some degree in the knee of the 
ape, whilst in man of course the popliteus acts only as a flexor. 
Melzer’ considers the homologies to be as follows : 
Supinator longus......-.---6-5yoo Gntromnemie oe head. 
Pronator teres (humeral head) f Louter head. 
Pronator teres (ulnar head). ............Popliteus. 
Macalister* looks upon the inner head of the gastrocnemius as the 
homologue of the pronator radiiteres. It is superficial and not deep like 
the popliteus, and this fact he considers to be in favour of his hypothesis. 
The Plantaris was absent and it would appear that the muscle is very 
rarely present in anthropoid apes. The only instance in which it was 
found in the Orang was in that dissected by Sandifort, who is stated by 
Fick* to have found it in that animal. It is frequently absent in man. 
Whilst the plantaris is almost invariably absent in anthropoid apes, it is 
well-developed, according to Bischoff,’ in the lower apes (Cynocephalus, 
Cercopithecus, Macacus and Pithecia), forming a strong tendon passing 
under the posterior part of the os calcis, and it may be followed into the 
sole where it joins the plantar fascia. Bischoff,’ however, found a slightly 
developed plantaris arise on both sides in the Chimpanzee. and in this 
animal, too, it has been described by Macalister’ as present on the right 
side in one Chimpanzee and absent on both sides in another Chimpan- 
zee. It is, however, frequently absent in this animal, and with the 
exception of the one instance recorded by Sandifort in the Orang, it has 
not been found in any of the other anthropoid apes, although carefully 
sought for, and its absence recorded by various authors. The plant- 
aris in the leg doubtless corresponds to the palmaris longus in the fore- 
arm and has the same relation to the plantar fascia that the latter 
muscle has to the palmar fascia (see page 537). Thus Sutton* holds that 
the plantar fascia is derived from the degeneration of the distal end of 
x Loe, cit. 2; p..23. 
2 W. Melzer, ‘* Zur Homologie der menschlichen Extremitaten.” Internationale Monatsschrift fii 
Anatomie und Physiologie, Vol. XI, 1894, p. 209. 
3 A. Macalister, ‘‘On the Arrangement of the Pronator Muscles in the Limbs of Vertebrate Animals.” 
Journ, of Anat. and Phys., Vol. III, 1869, p. 340. 
WLOCsgCits Ty Ps Are 
5 Loc. cit. 1, p. 229, 
6 Loc. cit.2, p. 22. 
4 Loc. cit., p. 505. 
8 Loc. cit., p. «6, 
