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, ahove the tendon of the peroneus longus, whence it passes 

 on to its insertion into the base of the fifth metatarsal. 



The extensor longus hallucis (PI. XXV. fig. 3, 39) lies behind and partly beneath the 

 tibialis anticus (21), 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 (x), 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 (PI. XXV. figs. 1 & 3, 35) 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 ( 35' ) 

 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 (PI. 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. *') arising from the calcaneum, and 

 inserted into the metatarsal of the second digit and that of the third digit, expanding in 

 each upon the capsule of the joint of the first phalanx. There is a small 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 (PI. XXIV. fig. 3), presents an oval 

 form, with the small and obtusely pointed end forwards ; it measures 2 inches 2 hnes 

 in length, 1 inch 7 lines in greatest breadth, and 1 inch 3 lines in height. The cere- 

 brum (ib. fig. 4, a) covers the olfactory lobes (ib. c) in front, and about one-third of the 

 cerebellum (ib. b) behind. The length of the cerebrum is 1 inch 10| lines ; its breadth 

 is I inch 6 lines, each hemisphere measuring 9 lines across 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 6. The length of the fissure «, to its bifurcation, is 1 inch ; it is of moderate 

 depth. External to it is the suprasylvian fissure (3, 3), in the form of an irregular arch : 



