, MUSCLES ON FRONT AND INNER ASPECT OF FOREARM. 323 
than the previous hgament. It consists of an oblique band of fibres about an 
inch broad, attached externally to the outer side of the lower end of the radius, 
and internally to the lower end of the ulna, the carpus, and the internal lateral 
ligament of the wrist. It is covered by veins, by the radial nerve, and by the 
dorsal branch of the ulnar nerve. Six compartments are formed beneath it by the 
attachment of septal bands to the radius and ulna. Each compartment is provided 
with a synovial membrane, and they serve to transmit the extensor tendons of the 
wrist and fingers in the following order from without inwards :— 
Extensor ossis metacarpi pollicis and extensor brevis pollicis. 
Extensores carpi radiales, longior and brevior. 
Extensor longus pollicis. 
Extensor communis digitorum and extensor indicis. 
Extensor minimi digiti. 
. Extensor carpi ulnaris. 
The thin deep fascia of the dorsum of the hand is lost over the expansions of 
the extensor tendons on the fingers. Beween the metacarpal bones a strong 
layer of fascia covers and gives attachment to the interossei muscles. 
The palmar fascia is of considerable importance. In the centre of the palm 
it forms a thick triangular membrane, the apex of which joins the lower edge of 
the anterior annular ligament, and receives the insertion of the tendon of the 
_palmaris longus muscle. The fascia separates below into four slips, one for each 
finger, connected together by transverse fibres, forming beneath the webs of the 
fingers the superficial transverse metacarpal ligament. Beyond this each slip 
separates into two parts, to be connected to the sides of the metacarpo-phalangeal 
joints and the first phalanx of the inner four digits. In the cleft between the two 
halves of each slip the digital sheath is attached and extends downwards on to the 
finger. The lateral borders of this triangular central portion of the palmar fascia 
are continuous with thin layers of deep fascia, which cover and envelop the muscles 
of the thenar and hypothenar eminences. The inner border gives origin to the 
palmaris brevis muscle. 
The digital sheaths are tubular envelopes extending along the anterior aspect 
of the digits and enclosing the flexor tendons. Each consists of a continuous 
fibrous sheath attached to the lateral borders of the phalanges and interphalangeal 
joints, and continuous above with the palmar fascia. Opposite each interphalangeal 
articulation the digital sheath is loose and thin; opposite the first two phalanges 
(the first only in the case of the thumb) it becomes extremely thick, and gives 
rise to the ligamentum vaginale, which serves to keep the tendons closely apphed 
to the bones during flexion of the fingers. Within each digital sheath are the flexor 
_ tendons, enveloped in a synovial membrane which not only envelops the tendon 
_ but also lines the interior of the sheath. The synovial membranes of the digital 
sheaths extend a short distance upwards in the palm, and in some cases com- 
~ municate with the large synovial membranes lining the flexor tendons beneath 
the annular ligament. There may be a separate distinct synovial membrane for 
each digit ; but most commonly only the sheaths for the three middle digits have 
Separate synovial membranes; those for the flexor longus pollicis and for the 
flexor tendons of the little finger communicate usually with the synovial mem- 
branes placed beneath the anterior annular ligament. 
DOVE 29 pO 
~ Ge a2 
THE MUSCLES ON THE FRONT AND INNER ASPECT OF 
THE FOREARM. 
The pronator and flexor muscles which lie on the front of the forearm occupy 
different levels, and are divisible into two main groups, superficial and deep. 
SUPERFICIAL MUSCLES. 
_ The superficial muscles form the prominence on the front and inner side of 
the forearm, and all take origin in whole or part by means of a common tendon 
from the internal condyle of the humerus. The group comprises five muscles— 
