THE BRACHIAL OR AXILLARY ARTERIES. 659 



Ulnar artery.— 'Much smaller than the radial, this vessel gives off, near its origin, the 

 interosseous artery, wliich sometimes proceeds directly from the humeral artery, and the calibre 

 of which 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 ulna and radius, underneath the 

 pronator quadratus, and is prolonged to the lower third of the forearm, where it separates 

 into two branches — the anterior and posterior interosseous arteries, after throwing off on its 

 way several branches, mostly anterior, which enter the antibrachial muscles by traversing the 

 space comprised between the two bones of the forearm, 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 rauiuscules 

 of the radio-palmar artery, and outwardly, the arborizations of a branch from the posterior 

 interosseous artery, forming with these vessels a wide-meshed plexus, from which definitely 

 proceed several filaments that join the dorsal interosseous 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 pronator quadratus, 

 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 with a thin filament from the radio-palmar artery. This arch 

 supplies, with some ramuscules destined to the muscles of the hand (or paw), eight inter ossf.ous 

 metacarpal arteries— four posterior or palmar, wliich are united by their inferior extremity 

 with the collaterals of the digits, after giving several divisions to the muscles of the hand ; and 

 four anterior or dorsal, traversing the superior extremity of the intermetacarpal spaces, like 

 the perforating arteries in Man, joining the anterior interosseous branches of the forearm, 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. Lying 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 the posterior antibrachial inter- 

 osseous artery, formg the superficial palmar arch, from which escape four branches — the 

 palmars or collaterals of the digits. Tliese are at first situated between the perforatus and 

 perforans tendons, and reach tlie superior extremity of the interdigital spaces, where they 

 receive the metacarpal interosseous arteries, and comport themselves in the following manner : 

 the internal goes to the thumb ; the second — counting from within outwards— gains the con- 

 centric side of the index; the third, the largest, divides into two branches which lie alongside 

 the great digits ; the last goes to the external digit. 



Comparison of the Axillary Arteries in Man with those of Animals. 



The arteries of the thoracic limbs and liead arise separately from the arch of die aorta ; 

 consequently, in Man there is no anterior aorta. 



The vessel of the liinb that represents the axillary of animals is here resolved into two 

 portions : the subclavian artery and axillary artery. 



The Subclavian Artery has not the same origin on both sides; on the right it arises 

 from the aorta by a trunk common to it and the carotid of that side — the arteria innominata; 

 while the left is detached separately from the most distant part of the aoriic aruh. The 

 subclavian vessels extend to the inferior border of the clavicles, and furnish seven important 

 collateral branches, wliich are present in the domesticated animals. They are — 



1. The vertebral artery, situated in the vertebral foramina of the cervical vertebrae, as far 

 as the axis ; there it anastomoses, as in Solipeds, with a branch of the carotid, enters the 

 spinal canal by the ioramen magnum, and unites with its fellow at the lower border of the 

 pons Varolii to form the basilar artery which, in the Horse, comes from the cerebro-spinal 

 artery of the occipital. 



