THE BRAC3IAL OB AXILLABT ARTERIES. 569 



at the inferior extremity of the lateral bones by anastomosing in full 

 canal with a branch of the collateral of the cannon. They furnish some 

 ramifications to the suspensory ligament which covers them, and several 

 tendinous and cellulo-cutaneous twigs ; one supplies the medullary artery 

 of the principal cannon bone (Fig. 283, 7). 



6. The anterior interosseous arteries arise from nearly the same point as 

 the preceding, one outwards, the other inwards, turning back round the head 

 of the lateral metacarpals to place themselves in the groove which separates 

 these from the principal metacarpal bone, on their external or dorsal face, 

 after having thrown off several anastomosing ramuscules which communicate 

 between the two arteries in front of the upper extremity of the median meta- 

 carpal bone, or with the terminal branches of the anterior radial and the 

 interosseous arteries of the fore-arm. By their terminal extremity, these two 

 arteries anastomose with a branch of the collateral of the cannon — that 

 which receives the posterior interosseous arteries (Mg. 282, 7', 8). 



The dorsal interosseous arteries, although much finer than the palmar (in 

 Solipeds these arteries are quite rudimentary), nevertheless furnish collateral 

 divisions destined for the anterior tendons of the metacarpus, the periosteum, 

 the connective tissue, and the skin. They often communicate with the 

 posterior arteries by deep branches, which cross the intermetacarpal 

 ligaments. 



Yariations. — The existence of the interosseous metacarpal arteries, their 

 position, and their anastomoses with the inferior extremity of the collateral 

 of the cannon, are constant ; though this is not the case with regard to their 

 origin, or the source from which they arise. In the typical description we 

 have given, we have considered them all as being furnished by the radio- 

 palmar artery ; but it is necessary to add that one of the four, the external 

 dorsal, often comes directly from the arterial branch that, from the supror- 

 carpal arch, descends along the carpus to concur in forming the suhcarpal 

 arch, by anastomosing with the radio-palmar, or rather with a branch of the 

 interosseous of the fore-arm. It is also necessary to add that these meta- 

 carpal arteries sometimes arise together from one large branch furnished by 

 the collateral of the cannon, at the superior extremity of the metacarpus, 

 and which receives the now rudimentary radio-palmar artery, as well as that 

 given off by the supracarpal arch ; so that we may have two superposed 

 supracarpal arches. We have met other anomalies which need not be noticed 

 here, as they are without interest. 



2. Second Terminal Branch of the Posterior Badial, or Collateral Artery of the 

 Gannon} (Fig. 283, 9.) 



The collateral artery of the cannon continues, in its volume and direction, 

 the posterior radial artery. It passes, with the flexor tendons, under the 

 carpal arch, and descends on the inner side of these tendons, accompanied 

 by the internal plantar nerve, to above the fetlock and near the great 

 sesamoid bones, where it bifurcates into the digital arteries. 



Collateral branches. — We observe : 



1. Near the origin of the artery, and very often from the posterior radial 

 artery itself, a branch which anastomoses above the pisiform bone with the 

 epicondyloid artery, forming an arch whose convexity is inferior (Fig. 283, 3), 

 and which has been already noticed as the supracarpal or superficial palmar 

 ' This artery, the superficial plantar of Kigot, represents one of the metacarpal 

 palmar branches furnished by the superficial pahnar arch in Man and other pentadactyloua 

 animals. 



