THE UPPER LIMB 369 



Palmar Fascia. — The palmar fascia is arranged in three divisions 

 — central and two lateral. 



The central division is triangular, the apex being towards the 

 wTist, where it is continuous with the tendon of the palmaris 

 longus, and attached to the front of the anterior annular ligament 

 close to its lower border. The superficial fibres of this division are 

 longitudinal, and the deep fibres transverse, the latter being most 

 conspicuous between the diverging digital processes. The base is 

 directed towards the roots of the four inner fingers, on approaching 

 which the fascia divides into four digital processes. These diverge 

 and pass to join the sheaths of the flexor tendons on the fronts of the 

 fingers. Each process gives fibres to the superficial transverse liga- 

 ment and skin of the clefts of the fingers. Each also gives ofl a deep 

 expansion at either side, which joins the transverse metacarpal 

 ligament at either lateral margin of the head of a metacarpal bone. 

 In this way short canals are formed for the superficial and deep 

 flexor tendons on their way to the fronts of the fingers. Between the 

 diverging digital processes three intervals are left, in which the digital 

 arteries and nerv^es and limibricales muscles make their appearance ; 

 and, as stated, the transverse fibres are here conspicuous, where they 

 lie superficial to these structures. The central division is bound to 

 the skin by fibrous processes which enclose spaces containing the 

 lobules of the superficial fascia. Its deep surface is related to the 

 great palmar bursa. At either side it gives off a deep septimi 

 which joins the interosseous fascia. The outer septum is placed 

 betw^een the thenar muscles and the centre of the palm, where the 

 flexor tendons and digital vessels and nerves lie, and it is. pierced 

 by the digital nerves for the sides of the thumb and index finger. 

 The inner septum is placed between the hypothenar muscles and 

 the centre of the palm, and it is pierced by the digital branches of 

 the ulnar nerve, and by a portion of the superficial palmar arch. 

 In this way a large central fascial canal is formed, which contains 

 1 the superficial palmar arch and its digital branches, the digital 

 I nerves, the superficial and deep flexor tendons, and the limibricales. 

 On either side of this central canal are the thenar and hypothenar 

 j canals, containing the short muscles of the thumb and of the 

 little finger. The central division of the palmar fascia serves as 

 j an important protection to the superficial palmar arch and the 

 ' digital arteries and nerves. From its great strength and capability 

 ' of resistance it has an important bearing on the course taken by 

 ■ t pus in a palmar abscess. 



1 The central division represents the expanded portion of the 

 : i tendon of an original superficial flexor muscle of the fingers. 



The external or thenar division is thin, and covers the thenar 



; I muscles. Superiorly it is connected with the tendon of the palmaris 



1 [ longus and anterior annular ligament, and it receives an accession 



I of fibres from the tendon of the extensor ossis metacarpi pollicis. 



'Inferiorly it blends with the sheath of the tendon of the flexor longus 



'pollicis on the front of the thumb. 



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