THE BRACHIAL OH AXILLARY ARTERIES. 573 



costal or superior intercostal arteries tke first passes between the two anterior ribs ; tho 

 second m front of the fii-st ; the thii-d across the internal face of the first, second, and 

 third ribs near their cartilages, where it emits ascending and descending intercostal 

 blanches. 



2. The vertebral artery, anastomosing, as in Solipeds, with a retrograde branch from 

 the occipital artery ; it supplements, Iq very great part, the superior cervical, whose 

 volume is diminutive, and which is only distributed to the posterior part of the neck. 



3. The inferior cervical artery, giving off the pectoral branches. 



4. Tlie internal thoracic artery, remarkable for its large volume, and for a superficial 

 division chiefly destined to the mammse, which joins an analogous branch from the 

 external pudic artery. 



5. An external thoracic branch, whose origin more resembles that of the siwer- 

 scapular artery, which appears to be absent. 



6. The subscapular artery. After furnishing this vessel, the brachial trunk is pro- 

 longed by the humeral artery, which we will now examine in detail. 



HuMERAi Artery.— Placed at first immediately beliiud the coraco-radial or biceps 

 muscle, this vessel descends beneath the round pronator, and divides at the superior 

 extremity of the radius into two terminal branches ; these are the ulnar and radial 

 arteries. 



It detaches on its course collateral branches, analogous to those which have been 

 described for Solipeds, and among which is a thin vessel, a vestige of the anterior radial 

 artery, that passes beneath the terminal extremity of the biceps to supply the muscles 

 covering, anteriorly, the articulation of the elbow. 



Ulnar artery. — Much smaller than the radial, this vessel transmits, near its origin, 

 the interosseous artery, which sometimes proceeds du-ectly from the humeral artery, and 

 whose calibre always exceeds, in animals, that of the ulnar artery. The latter is directed 

 obliquely outwards and downwards, passing under the perforans, and gains the internal 

 face of the anterior ulnar or oblique flexor of the metacarpus, where it lies beside the 

 ulnar nerve, to descend with it inside the unciform bone, and join the posterior interosseous 

 artery, or one of its terminal branches. On its track it gives off a number of muscular 

 or cutaneous branches, several of which anastomose with the internal collateral artery 

 of the elbow, as well as with divisions of the radial artery. 



Interosseous artery. — This artery is placed between the cubitus and radius, under- 

 neath the square pronator, and is prolonged to the lower third of the fore-arm, where it 

 separates into two branches — the anterior and posterior interosseous arteries, after 

 abandoning on its way several branches, mostly anterior, which enter the antibrachial 

 muscles by traversing the space comprised between the two bones of the fore-arm, the 

 principal escaping by the radio-ulnar arch. 



The anterior interosseous artery, after passing between the radius and ulna, descends 

 on the anterior face of the carpus, where its divisions meet, inwardly, the collateral 

 ramuscules of the radio-palmar artery, and outwardly, the arborisations of a branch from 

 the posterior interosseous artery, forming witk these vessels a wide-meshed plexus, 

 from which definitively proceed several filaments that join the dorsal iuterosseous 

 metacarpal arteries. 



The posterior interosseous artery may be regarded, by its volume and direction, as the 

 continuation of the interosseous trunk. After emerging from beneath the square pronator, 

 it detaches an internal flexuous branch anastomosing with the radio-palmar artery, then 

 several external musculo-cutaneous branches ; after which it is placed within the 

 pisiform bone, where it divides into two branches, after receiving the ulnar artery. The 

 smallest of these branches anastomoses by inosculation with the superficial palmar arch; 

 the other, larger and deeper-seated, is carried in front of the flexor tendons, beneath the 

 aponeurosis covering the interosseous muscles, across the superior extremity of these, and 

 so forming the deep palmar arch, which unites witli a thin filament from the radio-palmar 

 artery. This arch supplies, with some ramuscules destined to the muscles of the hand 

 (or paw), eight interosseous metacarpal arteries : four posterior or palmar, which are united 

 by their inferior extremity with the collaterals of the digits, after giving several divisions 

 to the muscles of the hand; and four amterior or dorsal, traversing the superior extremity 

 of the intermetacarpal spaces, like the perforating arteries in Man, joining the anterior 

 interosseous branches of the fore-arm, and descending afterwards into the intermetacarpal 

 spaces, to unite with the collateral arteries of the digits at the metacarpo-phalangeal 

 articulations. 



Radial artery: the posterior radial of the other animals. Lymg alongside the 

 long flexor of the thumb and the perforans muscle, this artery follows the inner face of 

 the'perforatus muscle, and curving outwards to be united to a branch from tlie posterior 

 antibrachial interosseous artery, forms the superficial palmar arcade, from which escape 



