68 PROFESSOR OWEN ON THE AYE-AYE. 
the outer malleolus, with that of the peroneus longus, and then through a distinct 
sheath on the calcaneum, above the tendon of the peroneus longus, whence it passes 
on to its insertion into the base of the fifth metatarsal. 
The extensor longus hallucis (Pl. XXV. fig. 3, 99) lies behind and partly beneath the 
tibialis anticus (24), arises from the outer and fore surface of the tibia, from near the head, 
a short way down; converges to a tendon about the lower third of the leg, which 
passes through a sheath in the transverse ligament (a), is bound down on the tarsus by a 
small ligamentous sheath attached to the naviculare, and thence passes along the outer 
part of the phalanges of the hallux to the ungual one, into which its terminal expansion 
is inserted. 
The extensor communis digitorum (Pl. XXV. figs. 1 & 3, 5) arises by a distinct 
head from near the head of the fibula, and by a stronger portion from the upper half 
of the fibula and the interosseous fascia. The tendon from the first portion divides, to 
be attached to the second and third toes; that from the second part of the muscle ( ss’) 
passes through a distinct sheath, and divides to go to the fourth and fifth toes. Both 
primary tendons, before their division, are expanded upon the tarsus and partially 
united to each other. 
The extensor brevis hallucis (Pl. XXV. fig. 3, «°) arises from the upper and tibial 
side of the calcaneum ; its fleshy fibres converge as they pass beneath the tendons of 
the long extensor to a tendon which is attached to the metatarsal of the hallux. 
There are similar but smaller short extensors (ib. «1) arising from the calcaneum, and 
inserted into the metatarsal of the second digit and that of the third digit, expanding in 
each upon thé capsule of the joint of the first phalanx. There is asmall abductor and an 
adductor (ib. fig. 2, «2) of the hallux. Interosseous muscles serve to extend and abduct 
the fourth and fifth digits. 
§ 6. The Brain. 
The brain of the Aye-aye, viewed from above (Pl. XXIV. fig.3), presents an oval 
form, with the small and obtusely pointed end forwards ; it measures 2 inches 2 lines 
in length, | inch 7 lines in greatest breadth, and 1 inch 3 lines in height. The cere- 
brum (ib. fig. 4, a) covers the olfactory lobes (2b. c) in front, and about one-third of the 
cerebellum (2b. 8) behind. The length of the cerebrum is 1 inch 10} lines; its breadth 
is 1 inch 6 lines, each hemisphere measuring 9 lines acress its broadest part, which 
is at about the junction of the middle with the hinder third. 
The hemispheres are simply and symmetrically convoluted ; each shows the longitu- 
dinal fissure (2, 2), which slightly diverges from its fellow as it advances, and bifurcates,— 
one branch curving forward and inward, bounding anteriorly the medio-longitudinal con- 
volution a; the other bending outward and downward to bound the suprasylvian convolu- 
tion b. The length of the fissure a, to its bifurcation, is 1 inch; it is of moderate 
depth. External to it is the suprasylvian fissure (s,s), in the form of an irregular arch : 
