578 DR. J. MURIE ON THE ANATOMY OF THE SEA-LION, 
the os calcis and the scaphoid, and continues to the distal border of the tarsus, where it 
forms a broad, strong ligamentous union with the flexor longus hallucis. From the 
superficial surface of this broad aponeurotic fascia the lumbricales are given off. The 
flexor longus digitorum appears to give tendons to the four outermost digits; of these 
that to the second, third, and fourth digits is strengthened by tendinous fibres from 
the flexor longus hallucis; together they form the perforans. 
The flexor longus hallucis (F.1.h) arises from the head and upper fourth of the shaft of 
the fibula. Its fleshy belly, as already said, crosses the flexor longus digitorum, and is 
itself partly covered above by the single gastrocnemius. Its tendon, which commences 
above the malleolus, runs in the outermost groove of the two, behind the tibial malleolus, 
and, on the plantar surface of the pes, joins, as aforesaid, the flexor longus digitorum. A 
strong tendon pursues its course to the hallux, being inserted into the distal phalanx by 
an expanse of aponeurotic fascia. But besides this the flexor longus hallucis, as already 
mentioned, sends tendinous slips, which unite with those of the flexor longus digitorum, 
supplying the second, third, and fourth digits. 
Interossei of Hind Foot.—These exist only on the plantar surface of the pes, and are 
true flexores breves; they are but partially seen on the dorsal surface, and even there 
only when the strong fascia between the metacarpal bones has been removed. There is 
a superficial and a deep layer, perfectly distinct from each other as in the manus. 
Superficial Layer. This, one continuous broad flat expanse of fleshy fibres, some- 
what semilunar or crescentic in shape, stretches from the hallux to the fifth digit. 
It arises from the deep plantar fascia at the proximal ends of the metacarpals; and 
its semilunar anterior free border reaches to about the middle of the metacarpal bones 
of the second, third, and fourth digits (see fig. 38, dotted line). 
One horn of the crescent, the larger and thicker of the two, proceeds to the hallux, 
partly joining, or lying on the outer side of, the interosseus muscle of the hallux, and, 
running on with it in the form of a tendon, inserted into the distal end of first meta- 
carpal (S.z'). The second, outer horn or belly (Sc*) goes to the inner side of the fifth 
digit, and terminates fleshy at the distal extremity of the fifth metacarpal; but strong 
interarticular fascia is continued over the joint to the proximal end of the first phalanx. 
Use. ‘These approximate the metacarpal bones, and are also short flexors. 
Deep Layer. ‘This consists of one single and four double muscles. Ist. ‘The single 
interosseus muscle (1) supplying the hallux has the largest belly and is the longest of < 
the deep interossei. It arises by tendon from the internal cuneiform bone, and is 
inserted into the fascia covering the metacarpo-phalangeal joint of the hallux. 2nd. 
The second, deep and double, interosseus muscle (2) arises from the proximal ends of 
the first and second metacarpals. The smaller moiety of this muscle, that next the 
hallux, has also a partial origin or attachment to the superficial layer of interosseous 
fibres and hallucial metacarpal. Insertion by tendon and fascia into the sesamoid 
cartilage at the metatarso-phalangeal joint. 3rd, 4th, and 5th. Double interossei 
