156 THE SUPERIOR EXTREMITY 



the medial side of the apex of the hook of the os hamatum. 

 A short distance distal to the hook of the os hamatum it 

 turns laterally, pierces the septum which separates the medial 

 from the intermediate fascial compartment of the palm, and 

 crosses the intermediate compartment, lying between the 

 intermediate part of the palmar aponeurosis, which is super- 

 ficial to it, and the terminal branches of the median nerve 

 and the flexor tendons, which are deep to it. At the lateral 

 border of the intermediate fascial compartment it unites with 

 a branch of the radial artery, either the superficial volar, or 

 the radialis indicis, or the princeps pollicis. The arch 

 lies, therefore, in the medial and intermediate fascial com- 

 partments of the palm. In the medial compartment it lies 

 upon the flexor brevis and opponens digiti quinti muscles and 

 is covered by the palmaris brevis. In the intermediate 

 compartment it lies upon the flexor tendons and the digital 

 branches of the median nerve, and it is covered by the 

 intermediate part of the palmar aponeurosis. 



As the ulnar artery lies on the transverse carpal ligament, 

 before it becomes the superficial volar arch, it gives off a pro- 

 funda branch which passes deeply into the palm, with the 

 deep division of the ulnar nerve, between the abductor 

 digiti quinti muscle medially and the flexor digiti quinti 

 brevis laterally. That branch will be traced in the deep 

 dissection of the palm. From the superficial arch itself 

 small twigs are given off to the adjacent tendons and fascia, 

 but the chief branches are the four digital arteries which 

 spring from the convexity of the arch. The first of the four 

 remains undivided. It runs to the medial border of .the 

 little finger, along which it passes to the terminal phalanx. 

 The other three branches, 2nd, 3rd, 4th, pass towards the 

 interdigital clefts, where each divides, at the level of the 

 bases of the first phalanges, into two branches, which supply 

 the sides of the adjacent fingers, the second supplying the 

 little and ring fingers, the third the ring and middle, and the 

 fourth the middle and index fingers (Figs. 68, 69). 



There are certain practical points to be noted in associa- 

 tion with the digital arteries. The first crosses the lateral 

 branch of the superficial division of the ulnar nerve and the 

 short muscles of the little finger The undivided parts of 

 the second, third, and fourth lie in line with the inter- 

 digital clefts between the fingers ; each is situated between 



