Bones.—The head of the humerus assumes a very characteristic appearance as a con sequence of this peculiar disease, and acquires a form which cannot be easily niistaken for the effects of any other disease or accident. The usual angle at which the head and neck of the humerus join the shaft of the bone is often altogether effaced ; so that instead of the axis of the head and neck of the humerus being directed, as it normally is, upwards, inwards, and backwards, it seems to run ver tically, or, as it were, in a continuous line with that of the shaft of the bone. The articular surface is usually much enlarged, and in the ordinary form of this disease occu pies the whole summit of the humerus, ex tending itself even over the greater and lesser tuberosities and the highest part of the bi cipital groove ; effacing in this direction part or the circular line which marks the anato mical neck of the humerus and insertion of the capsular ligaments. Some of the articular cartilage is removed from the head of the bone, which, in some places, presents a porous appearance (fig. 428.).
In other parts, in place of the cartilage, there is a polished ivory-like surface. The portion of the bone which thus presents this polished surface is the very summit of the humerus ; and this is the part of the bone which will be found evidently to have been for years in habitual contact with the under surface of the acromion and coracoid pro cess, where these bones assist in forming por tions of the new and abnormal cavity for the reception of the head of the humerus. The basis of the head, in the line where it joins the shaft of the humerus, is studded round by granular osseous productions, which give to it a characteristic appearance Cit. 428.). By these vegetations of bone, we are reminded of the analogous appearance which the corona of the head of the femur presents when affected by the same species of morbid action *; but of course much variety may be expected to be found in the form the head of the humerus will assume under the influence of this disease : we have found the articular surface in scone cases formed completely on the sutnmit of the hu merus, sometimes on the side of the head. Very generally the head of this bone is much enlarged, but exceptions to this rule occur. One of the most remarkable alterations of form we have noticed as the result (as we imagine) of this disease we found in the anatomical museum at Leyden. In the spe cimen to which we allude, the head of the humerus appears bifurcated at its upper part, or divided longitudinally into two surfaces for articulation with the scapula.t Lastly, we have to advert to the anatomi cal characters of the new and abnormal socket formed for the reception of the altered head of the humerus. This new cavity is com posed of two portions, which however will be found to have become almost continuous with each other. The original glenoid cavity (ge nerally much enlarged) forms one of these portions ; the coraco-acromial vault the other.
By the coraco-acromial vault we mean a concave surface, looking downwards, formed internally by the coracoid process, and ex ternally by the acromion ; the intervening space being filled up in front by the proper triangular ligament of the scapula, and com pleted behind by a portion of the under-sur flice of the acromial end of the clavicle This coraco-acromial arch in the normal state overhangs much the head of the humerus, and its inferior surface is not articular, but, on the contrary, is separated from the head of the humerus, which is beneath it, by an in terval of about three or four lines, measured in vertical height. This interval is normally
occupied by the long tendon of the biceps and the capsular ligament, as they pass from the upper margin of the glenoid cavity to the hu merus—the capsular ligament having above it the tendon of the supra-spinatus, a special bursa mucosa, much cellular tissue, and the fibrous bands, which pass from the humerus to the coracoid and acromial processes.
Under the influence of the most usual form of this disease, all these parts intervening between the head of the humerus and the coraco-acromial arch or vault are absorbed ; and the superior extremity of the head of the humerus at length comes into immediate con tact with the concavity of the arch. The first effect of this morbid process in bringing about the remarkable changes which we have been describing, may be to cause the absorp tion of those tendons, viz. the supra-spinatus and the long tendon of the biceps, which pass over the head of the humerus, and which, by virtue of their muscular attachments, restrain within proper limits the degree of elevation * which the head of the humerus is normally susceptible of. When, however, these tendons are absorbed, and consequently the muscles to which they belong have lost all power of re pressing the humerus, the latter is then drag ged upwards, and its head being constantly pressed against the under-surface or concavity of the coraco-acromial arch, not only do the processes of the scapula which form this arch at length show manifestly the effects of fric tion, but the outer portion of the acromial end of the clavicle does so equally. All these portions of bone are rendered con cave, and are usually covered by a porcelain like deposit, corresponding to an analogous polished surface which covers the convexity of the summit of the humerus. In many cases in which the shoulder joint has long been the seat of this chronic disease, the acromion process has been found traversed in the line of junction of its epiphysis, by a complete interruption of its continuity, as if fractured : we say as if fractured, for we are convinced that this solution of continuity of the acro mion process is not really a fracture produced by violence, but a lesion, which so frequently exists in combination with chronic rheumatic arthritis of the shoulder, that we are com pelled to look upon it, in these cases, as a peculiar organic change, the result of chronic rheumatic disease. We do not pretend to account for the separation of the acromion process into two portions ; nor can we say why it is that the division usually occurs in the original line of the epiphysis, particularly at the late period of life at which we generally witness this phenomenon. In some of these cases we have found the acromion in a state of hypertrophy; in others in a state of atro phy; but in no case did there seem to be any attempt at ossific deposition on the contigu ous surface of the separated portions of the acromion, a circumstance which tnight be ex pected if a fracture had occurred.