228 



RADIO-ULNAR ARTICULATIONS. 



crease of one is a diminution of some other 

 vessel or vice versa. 



The directness of these inosculations, and 

 the frequency of these resulting irregularities 

 together exert an important influence on sur- 

 gical practice, which may be regarded in three 

 points of view. Firstly, it necessitates unusual 

 care in the ordinary operations ; since we may 

 open an artery of dangerous size, where we 

 least expect it. Secondly, it renders opera- 

 tions undertaken on the vessels themselves 

 liable to immediate non-success ; for we 

 may find only a twig where we expect an 

 artery of influential magnitude. Thirdly, it 

 may also cause their mediate failure ; the 

 width and number of the anastomosing chan- 

 nels rendering deligation of a trunk useless, by 

 filling it in a very short space of time below 

 the ligature. Fortunately, however, the same 

 position that renders them more liable to in- 

 jury affords somewhat of a substitute for the 

 operation by also exposing them more directly 

 to external pressure. 



The diseases and injuries of the radial and 

 ulnar arteries scarcely offer peculiarities suffi- 

 cient to demand a special notice. 



Aneurism as the result of disease, an ex- 

 tremely rare occurrence in the brachial artery, 

 would appear to be here still more infrequent ; 

 and this remarkable immunity as compared 

 with the lower extremity has been differently 

 ascribed to a supposed greater vitality of the 

 vessels nearer the heart, or with better reason 

 to the less exposure of the arm to strains or 

 shocks. Even this explanation, however, has 

 so much imperfection about it, that it seems 

 better to avoid theorising on the subject until 

 more is known both of the physical relations 

 of the different tubes to their central engine, 

 and of the differences in the nature and ra- 

 pidity of the nutrition of their coats, which 

 may be presumed to exist. 



Fake aneurism may occur in any part of 

 their course as the result of puncture or inci- 

 sion of their coats; the sac of the tumour being 

 formed by the nearest investing fascia, and 

 lined by the areolar tissue of the neighbour- 

 hood condensed by the pressure of the con- 

 tents. These consist of blood, which is usually 

 in considerable quantities, and has experienced 

 more or less coagulation subsequently to its 

 discharge from the opening of the artery which 

 occupies some part of the inner surface of the 

 cavity. But neither in these points, nor in 

 the treatment usually adopted is there any- 

 thing which requires particular specification. 



The disease of the arterial system generally, 

 which constitutes so frequent and important a 

 part of the series of changes included in the 

 term " old age," of course includes these ves- 

 sels. Ossification of the radial artery is by no 

 means rare, although in this extremity it is 

 very unusual to find it occluding the tubes 

 or leading to senile gangrene. Here, from the 

 superficial position of this vessel, it is often a 

 valuable index by which an insight is afforded 

 into the condition of other and more important 

 arteries. In this latter stage of the change the 

 vessel is rather larger than normal, very hard, 



thick, and tortuous : while the impulse of the 

 heart communicated to it by its contents, and 

 tending to efface these abnormal curves, often 

 almost lifts it from its situation at each stroke. 

 In an earlier stage of the affection it is much 

 less easily recognised, but even here the tactus 

 eruditus may sometimes appreciate the change ; 

 and though it is perhaps difficult to translate 

 the sensation into words, such a pulse might 

 be paradoxically described as being at the 

 same time hard to the touch, and comparatively 

 soft and yielding to the pressure, while its 

 beats are associated with unusually little ex- 

 pansion, though they strike the fingers with 

 more force. 



( William Brinton). 



RADIO-ULNAR ARTICULATIONS. 



(Articulations radio-ulna ires Verbindungen des 

 Ellenbogenbeins mil der Speiche.} Wherever 

 the anterior extremity is modified to serve as an 

 instrument of prehension, one chief part of 

 the provision for greater freedom and facility 

 of movement occurs as the correlative modifi- 

 cation, not only of the two bones of the fore- 

 arm, but also of the articulations which mutu- 

 ally connect them at their upper and lower 

 extremities. In man, in whom the arm, losing 

 its locomotive, attains its most complete pre- 

 hensile development, the radius enjoys a very 

 considerable degree of motion around the ulna 

 by means of these joints. And by the alternate 

 preponderance of either of the two bones in 

 the wrist and elbow joints which are situated 

 at their opposite extremities, this mobility of 

 the radius is increased, while the freedom 

 of movement predicable of it becomes ex- 

 tended to the hand which occupies its distal 

 termination : and thus the rotatory movement 

 which is gradually superadded to the ordinary 

 flexion and extension of the limb finally 

 reaches its maximum. 



In each of these articulations we shall 

 separately describe, 1. Its anatomical consti- 

 tuents the several structures which serve to 

 allow of, or to limit, motion. 2. The result 

 of their functions the movements of the 

 joint. 



(1.) The upper radio-ulnar articulation 

 whose elements are the head of the radius, the 

 lesser sigmoid cavity of the ulna, the annular 

 ligament, and a synovial membrane. 



The round head of the radius represents in 

 shape the upper part of a cylinder, or rather a 

 horizontal segment of an inverted cone, which 

 becomes continuous below with the shaft of 

 the bone by means of a constricted neck. It 

 thus offers two articular surfaces: one, a shal- 

 low cup-shaped cavity which plays on the 

 radial tuberosity of the humerus : another, the 

 side of the cylinder, which has a linear mea- 

 surement of about a quarter of an inch at its 

 deepest part, where it corresponds to the lesser 

 sigmoid cavity of the ulna and ends below 

 in a prominent margin ; elsewhere it is nar- 

 rower ; and subsides more gradually into the 

 neck of the bone. These two smooth surfaces 

 merge into each other at the angle where the 

 base and circumference of the cylinder meet, 



