382 A MANUAL OF ANATOMY 



artery from the superficial arch to the inner side of the Uttle finger, 

 the junction taking place about the centre of the palm. In those 

 cases where the digital arteries from the superficial arch are awanting, 

 the palmar interosseous arteries may take their place. 



The recurrent branches, few and small in size, arise from the 

 concavity of the arch, and pass upwards to take part in the anterior 

 carpal rete. 



The superior perforating arteries, three in number, pass through 

 the upper ends of the inner three interosseous spaces between the 

 two heads of the corresponding dorsal interosseous muscles, and on 

 the back of the hand they join the dorsal interosseous arteries. 



Varieties of the Ulnar and Radial Arteries in the Hand. — i. The ulnar artery 



may be deficient in the number of digital branches furnished by the superficial 

 palmar arch, or the vessel may end as the profunda artery, in which latter case 

 there would be no superficial arch. Under these circumstances the deficiencies 

 are usually supplied by the palmar interosseous branches of the deep arch, 

 but sometimes by a large median and large superficial volar artery. 



2. The radial artery may be deficient in its normal branches, and the arteria 

 princeps poUicis and arteria radialis indicis may arise from the superficial 

 arch, from a median, or from a superficial volar, artery. 



Veins. — The deep palmar arch is accompanied by two venae 

 comites, which receive tributaries corresponding to the branches 

 of the arch. The destination of these venae comites on either side 

 has been already described in connection with the superficial 

 palmar arch. 



Summary of the Palmar Arches. — The superficial palmar arch is formed 

 mainly by the ulnar artery, being completed by the superficial volar of the 

 radial, or, if this fails, by a branch from the arteria radialis indicis, or arteria 

 princeps pollicis. Its digital branches lie over the interosseous spaces, so that, 

 to avoid them, incisions in the palm should be made in line with the centre of 

 a finger, and should not be prolonged farther upwards than the line indicating 

 the position of the superficial palmar arch. On the fingers the digital arteries 

 are placed laterally, so that in cases of whitlow an incision should be made 

 along the middle line of a finger. The superficial palmar arch is sometimes 

 joined by a large median artery, which is a branch of the anterior interosseous 

 high up in the forearm. In such cases, if the arch were to be punctured, and 

 if the haemorrhage could not be arrested by the graduated compress, it is 

 evident that ligature neither of the ulnar nor radial artery would suffice. In 

 order to arrest the circulation through a large median artery the ligature 

 would require to be placed on the brachial artery. 



The deep palmar arch is formed mainly by the radial artery, and is com- 

 pleted by the profunda branch of the ulnar. It lies about ^ inch above the 

 superficial arch. 



BACK OF THE FOREARM AND HAND. 



The cutaneous nerves, already described, are as follows : the 

 posterior branch of the musculo-cutaneous and the lower external 

 cutaneous branch of the musculo-spiral to the outer part, and the 

 posterior division of the internal cutaneous to the inner part. 



The deep fascia of the back of the forearm has been described in 

 connection with the anterior aspect, and the posterior annular 

 ligament will be presently referred to. 



