Mackintosh — On the Myology of the Genus Bradypus. 527 
synovial fold being continnous with the mncons ligament of the knee 
joint ; it is inserted by a weak tendon into the second metatarsal, and 
dorsal aponenrosis. In Professor Humphry's specimen the origin 
was from the external condyle of the femur, and the tendon of inser- 
tion was strong. 
Tibialis anticus (-20) has three heads in all, one from the upper 
two-thirds of the front of the tibia, one from the middle third of the 
fibula, and a third from the lower half of the same bone, the latter 
being larger than the tibial head, as Meckel describes. The same 
arrangement exactly obtained in Professor Humphry's specimen, 
whilst Professor Macalister says that the fibular head from the middle 
third is very diminutive, and describes the second fibular head as 
extensor hallucis proprius. The insertion of the first and second heads 
is by a single tendon into the base of the inner metatarsal and ento- 
cuneiform (Professor Humphry) ; the third head has a distinct 
tendon inserted into the first phalanx of the first digit (entocuneiform 
and base of Met. I, Professor Humphry). 
Extensor hallucis ('09) is a small oblique muscle arising from the 
lower fourth of the front of the fibula underneath peroneus tertius, 
and inserted into the first phalanx of the first digit. In Professor 
Humphry's specimen the insertion was threefold, two tendons going 
to the last phalanges of digits one and two, and a third to the proximal 
phalanx of the first digit. 
Extensor brevis digitorum arises from the lower extremity of the 
fibula and from the dorsal aspects of the tarsals and metatarsals; its 
tendon dividing into three parts joins the dorsal interossei, and is 
inserted into the three digits. Professor Macalister found the origin 
tibio-fibular, and the insertion single into the first phalanx of the inner 
digit, whilst Professor Humphry describes the origin as being only 
from the tarsals and metatarsals. 
Peroneus longus ('14) arises from the external condyle of the 
femur, and from the upper two-thirds of the fibula, passes downwards 
in front of the external malleolus, and is inserted into the outer 
metatarsal. 
Peroneus brevis (-02) arises from the lower half (lower two-thirds, 
Professor Macalister) of the external aspect of the fibula, and is inserted 
into the outer metatarsal. 
Peroneus tertius ('01) is as usual, running from the front of the 
fibula to the same bone as the two preceding muscles. 
Peroneo-metatarsalis in Arctopithecus takes origin from the outer 
malleolus, and is inserted into the spur-like process of the outer meta- 
tarsal, possibly representing a separate part of the last muscle. 
Peroneus quartus and peroneo-calcaneus are both absent. 
The femur and tibia are articulated in such a manner that they 
can be brought into one right line, and the knee joint has very strong 
external and internal lateral ligaments, the latter extending down as 
far as the upper point of trisection of the tibia ; the other ligaments 
presented nothing of interest. The interosseus membrane between 
