46 THE VOYAGE OF H.M.S. CHALLENGER. 



it turns round a deep groove in the cuboid, and is directed inwards across the sole. 

 It is inserted into the base of the first metatarsal bone. Two annular ligaments con- 

 fine the tendon in its passage downwards, viz., behind the external maleolus and upon the 

 outer aspect of the os calcis. In the sole of the foot it is not provided with a complete 

 sheath. 



In Thylacinus the peroneus longus presents an origin very similar to that in Cuscus. 

 Its tendon, however, is inserted into the ento-cuneiform bone, and as it winds round the 

 outer margin of the foot it is slightly attached by tendinous fibres to the base of the fifth 

 metatarsal bone. 



Dr. Georg Ruge, 1 in his elaborate memoir upon the extensor muscles of the leg and 

 foot, expresses his belief that the insertion of the peroneus longus into the inner margin 

 of the foot does not present the original condition of the muscle. To explain the course 

 of the tendon across the sole of the foot he advances the hypothesis that the original 

 insertion of the tendon was into the base of the fifth metatarsal, and that its progress 

 inwards has been caused by the fibres of insertion coming more and more into relation 

 with the plantar ligaments. In support of this theory he points to the Monotremata, in 

 which the tendon does not lie free in a sheath during its passage through the sole, but 

 is connected by thin membranous slips to the cuneiform bones, and in which also the 

 tendon is attached by a process containing half its fibres to the base of the fifth metatarsal. 

 In the Didelphys virginiania, Didelphys cancrivora, and the Dasyurus hallucinatus 

 he likewise noticed an attachment of the tendon of the peroneus longus to the 

 tuberosity on the base of the fifth metatarsal bone, whilst in the first of these animals 

 it presented additional attachments to the bases of the third and fourth metatarsal 

 bones. 



In Cuscus the tendon (PI. VI. fig. 6, p.t.) lies quite free in its sheath, and has no other 

 attachment except to the base of the first metatarsal bone ; in Thylacinus, as we have 

 seen, it is slightly attached to the base of the fifth metatarsal bone. 



Peroneus brevis. — In the Cuscus (PI. V. fig. 3, 6) this muscle arises by a narrow 

 pointed tendon from the anterior prominence of the head of the fibula ; it likewise 

 derives fibres from the intermuscular septum between it and the extensor communis 

 digitorum. In the Thylacinus it also takes origin from the shaft of the fibula in its upper 

 half, and in both animals it is inserted into the base of the fifth metatarsal by a tendon 

 which runs downwards behind the external maleolus and then along; the outer margin 

 of the foot. 



It seems to be the rule for this muscle to take origin from the shaft of the fibula as in 

 the Thylacine. Ruge 1 describes this in the Didelphys virginiana, Didelphys cancrivora, 

 and in Dasyurus hallucinatus. Dr. Ruge believes that the peroneus brevis is originally 

 derived from the outermost belly of the extensor brevis digitorum. 



1 A Research into the Group of Extensors of the Leg and Foot of Mammalia, Morph. Jahr., 1880. 



