RADIAL AND ULNAIl ARTERIES. 



227 



the same vessel which meets it just before 

 entering the metacarpal interspace. Where, 

 as is by no means infrequent, the radial is 

 larger than ordinary, its increased size is prin- 

 cipally expended in supplying, through a large 

 superficialis volae artery*, one or more of the 

 outer digital branches which usually come 

 from the superficial palmar arch: or, by means 

 of a dorsal metacarpal of unusual magnitude, 

 digital branches to the opposed sides of the 

 index and middle fingers. 



The high origin of the ulnar is contrasted with 

 that of the radial in another respect beside 

 that of its lesser frequency, since it is almost 

 always conjoined with an important difference 

 in the situation of the vessel in the forearm, 

 which lies superficial to the flexors ordinarily 

 covering it, and immediately beneath the 

 fascia: sometimes it is even sub-cutaneous. 

 Its course is also somewhat affected by this 

 origin, the vessel approaching the inner side 

 of the forearm at a higher point than usual : 

 in other cases, however, it possesses almost a 

 median position during the greater part of 

 this region, and only turns inwards to its 

 ordinary distribution near the wrist. 



In size, the ulnar artery is more frequently 

 diminished than increased by variations. The 

 decrease is compensated sometimes by a radial 

 vessel supplying one or more of its digital 

 branches or contributing to its palmar arch : 

 at others, its long branch which accompanies 

 the median nerve is enlarged to a vessel of 

 considerable size, which similarly assists it ; 

 while, in a few instances, the dilated anterior 

 interosseous has an analogous termination. 



The origin of the interosseous artery is 

 subject to some variation, being liable to occur 

 as a divarication from the radial or brachial, 

 or though rarely from the axillary: its en- 

 largement aids a deficient radial or ulnar 

 vessel, just as its diminutive size is supplied 

 by them. 



The branch with the median nerve enlarged 

 to a " median " artery, has been already men- 

 tioned ; it passes under the annular ligament 

 as it enters the hand, and may reinforce the 

 deficient radial or ulnar ; but most frequently 

 the latter of the two, by joining the super- 

 ficial palmar arch. 



Finally, as to the varieties in the hand, the 

 mode in which a diminished superficial palmar 

 arch is obviated, has already been described ; 

 and an unusually small deep arch is compen- 

 sated by the ulnar communicating, which is 

 generally little inferior in .size to the radial 

 contribution. For individually smaller digital 

 branches are substituted enlarged dorsal meta- 

 carpal ; and in the case of the magna polliris 

 the superficial palmar arch, the superficialis 

 vola 1 , or the median artery, may either of them 

 make up the deficiency. 



It may be desirable to attempt a generaliza- 

 tion of these special variations; in order to this, 

 let us return for a moment to the ordinary 



* Such a vessel, occupying from a high origin the 

 place of the artery, but more superficial than it, has 

 on this account been mistaken for a "hard" pulse, 

 and the patient depleted accordingly. 



anatomy of the vessels of the forearm and hand 

 considering them as a whole. Such a view 

 assisted somewhat, it must be confessed, by 

 our knowledge of these varieties, would dis- 

 cover in the forearm five longitudinal trunks, 

 all possessing some feature, whether of size, 

 length, or constancy, which especially recom- 

 mends them to our notice. They are the 

 radial, ulnar, and anterior interosseous vessels, 

 together with the posterior branch of this lat- 

 ter, and the branch with the median nerve. 

 The anastomosis and distribution of the ex- 

 tremities of most of these, forms around the 

 wrist an arterial circle which is much more 

 pronounced posteriorly.* In the hand, two 

 arches which are continuations of the larger 

 vessels occupy its surface of flexion, at diffe- 

 rent heights and depths ; defended from the 

 pressure inseparable from prehension by a 

 strong fascia, whose protective effect is aided 

 during flexion by a tightening muscle. They 

 join by anastomosis with the extremities of the 

 longitudinal vessels, or the imperfect anterior 

 carpal arch. Three branches run lengthwise 

 in most of the metacarpal interspaces ; one on 

 the dorsum from the posterior part of the 

 carpal circlet, two at different depths in the 

 palm from these arches ; the dorsal and deeper 

 palmar uniting at the superior extremities of 

 those intervals, and all three inosculating at 

 their inferior terminations near the clefts of 

 the fingers. 



All the varieties above mentioned would be 

 referrible to the increased development either 

 of one of these longitudinal branches, or ot 

 some portion of this complete and large anas- 

 tomosis. The several varieties are, in fact, an 

 exaggeration by turns of a different vessel ; 

 which in its course towards distribution may 

 recurn its contents to the ordinary channel by 

 any one of these series of inosculations ; whe- 

 ther it be the superficial or deep arch, the 

 posterior carpal arch, or finally, the superior 

 or inferior extremity of the aforesaid interos- 

 seous spaces. 



Thus from these vessels alone might be de- 

 duced the law, of which the origin of the ob- 

 turator from the epigastric, or the sublingual 

 from the facial, are familiar and important in- 

 stances; viz. that varieties of arteries occur 

 as the exaggerations of an ordinary anasto- 

 mosis -f- : while it is no less evident that the 

 deviations are compensative in the strictest 

 sense ; i. e. that the amount of blood entering 

 the limb is no ways affected, for that an in- 



* Unless we considered the deep palmar arch 

 as the anterior half of the carpal ring, a view which 

 the comparative infrequency of the minute "ante- 

 rior carpal arch " would almost allow of. 



t It may be urged against such a generalization, 

 " that it would scarcely include the varieties of those 

 vi'>M'U which immediately spring from the heart or 

 aorta: since anatomy shows the amount of their 

 ordinary anastomosis, and the number, size, and 

 regularity of the vessels effecting it, to be utterly 

 disproportionate to the magnitude of these vari- 

 ations.'' lint a reference to the aorta and branchial 

 arches, from which they are developed in the foetus, 

 would again include them in the category of dilated 

 inosculations. 



Q 2 



