416 ARTERIES. 



to which it is connected by a thin aponeurotic arch. It is accompanied by the 

 interosseous branch of the median nerve, and overlapped by the contiguous 

 margins of the Flexor profundus digitorum and Flexor longus pollicis muscles, 

 giving off in this situation muscular branches, and the nutrient arteries of the 

 radius and ulna. At the upper border of the Pronator quadratus, a branch 

 descends in front of that muscle, to anastomose in front of the carpus with 

 branches from the anterior carpal and deep palmar arch. The continuation of 

 the artery passes behind the Pronator quadratus, and, piercing the interosseous 

 membrane, descends to the back of the wrist, where it anastomoses with the 

 posterior carpal branches Q f the radial and ulnar arteries. The anterior inter- 

 osseous gives off a long, slender branch, which accompanies the median nerve, 

 and gives offsets to its substance. This, the median artery, is sometimes much 

 enlarged. 



The posterior interosseous artery passes backwards through the interval be- 

 tween the oblique ligament and the upper border of the interosseous membrane, 

 and down the back part of the forearm, between the superficial and deep 

 layers of muscles, to both of which it distributes branches. Descending to the 

 back of the wrist, it anastomoses with the termination of the anterior inter- 

 osseous, and with the posterior carpal branches of the radial and ulnar arteries. 

 This artery gives off, near its origin, the posterior interosseous recurrent branch, 

 a large vessel, which ascends to the interval between the external condyle and 

 olecranon, beneath the Anconeus and Supinator brevis, anastomosing with a 

 branch from the superior profunda, and with the posterior ulnar recurrent 

 artery. 



The muscular branches are distributed to the muscles along the ulnar side of 

 the forearm. 



The carpal branches are intended for the supply of the wrist-joint. 



The anterior carpal is a small vessel, which crosses the front of the carpus 

 beneath the tendons of the Flexor profundus, and inosculates with a corresponding 

 branch of the radial artery. 



The posterior carpal arises immediately above the pisiform bone, winding 

 backwards beneath the tendon of the Flexor carpi ulnaris ; it gives off a branch 

 which passes across the dorsal surface of the carpus beneath the Extensor tendons, 

 anastomosing with a corresponding branch of the radial artery, and forming the 

 posterior carpal arch ; it is then continued along the rnetacarpal bone of the little 

 finger, forming its dorsal branch. 



The deep or communicating branch arises at the commencement of the palmar 

 arch, passing deeply inwards between the Abductor minimi digiti and Flexor 

 brevis minimi digiti, near their origins ; it anastomoses with the termination of 

 the radial artery, completing the deep palmar arch. 



The digital branches, four in number, are given off from the convexity of the 

 superficial palmar arch. They supply the ulnar side of the little finger, and the 

 adjoining sides of the ring, middle., and index-fingers; the radial side of the index- 

 finger and thumb being supplied from the radial artery. The digital arteries at 

 first lie superficial to the Flexor tendons, but as they pass forwards with the digital 

 nerves to the clefts between the fingers, they lie between them, and are there joined 

 by the interosseous branches from the deep palmar arch. The digital arteries on 

 the sides of the fingers lie beneath the digital nerves; and, about the middle of the 

 last plialanx, the two branches for each finger form an arch, from the convexity 

 of which branches pass to supply the matrix of the nail. 



THE DESCENDING AOETA. 



The Descending Aorta is divided into two portions, thet horacic and abdominal, 

 in correspondence with the two great cavities of the trunk in which it is 

 situated. 



