ARTICULATION. 



251 



ments of this kind are composed of fibres 

 which are closely interwoven with each other, 

 and they sometimes receive accessions from 

 bundles of ligamentous fibres coming from 

 neighbouring bony prominences (these fibres 

 being generally called accessory ligaments.) 

 Capsular ligaments are not calculated to re- 

 strict the extent or direction of motion be- 

 tween the bones which they surround, and 

 we consequently find them only in that 

 kind of joint which admits of motion in all 

 directions, viz. the enarthrosis or ball-and- 

 socket joint, of which the only examples in 

 the human subject are to be met with in the 

 hip and shoulder. The internal or articular 

 surface of capsular ligaments is to a great 

 extent lined by one lamina of the synovial 

 membrane, which is reflected upon it from the 

 articular portion of the most moveable of the 

 bones which form the joint. 



Funicular ligaments are found in the form of 

 rounded cords or flattened bands : they exist 

 generally on the exterior of joints, very rarely 

 on the interior, and always externally to the sac 

 of the synovial membrane. They pass from 

 bone to bone, adherent sometimes to the syno- 

 vial membrane of the articulation, sometimes to 

 the intervening fibro-cartilage. In ginglymoid 

 joints they are always placed on the sides, and 

 are called lateral ligaments ; sometimes they 

 cross or decussate with each other, whence the 

 appellation crucial, and sometimes a ligament 

 of this class assumes a nearly circular course, 

 and forms a greater or smaller portion of the 

 circumference of a circle, the remainder of the 

 round being completed by the bone into which 

 the extremities of the ligament are fixed ; a 

 ring is in this way produced within which the 

 head, or a special process of another bone, is 

 enclosed, as is seen to be the case particularly 

 with the head of the radius in the superior 

 radio-ulnar articulation, and with the processus 

 dentatus in the joint between the axis and 

 atlas : the ligament in such instances is called 

 coronary. When a ligament is concealed in 

 the interior of a joint, although situated exter- 

 nally to the synovial sac, or, to speak more 

 correctly, in the space between the articular 

 surfaces, it is called an internal ligament, e. g. 

 the ligamentum teres of the hip-joint, the mu- 

 cous ligament of the knee, or the transverse 

 ligament of the same articulation. 



Elastic ligament. Hitherto we have been 

 examining ligamentous structure, one of whose 

 most prominent characteristics is the want of 

 elasticity ; but we now come to a kind of liga- 

 ment which forms a most valuable constituent 

 in the mechanism of some joints, and is emi- 

 nently distinguished for the great elasticity which 

 it possesses. It differs from ordinary ligament 

 by its yellow colour, (whence the French ap- 

 pellation tissu jaune,) as well as by its elasti- 

 city. We find it in the human subject most 

 developed in the ligamenta sub/lava of the 

 vertebrae. In joints, as elsewhere, this tissue 

 is employed to restore to the position of quie- 

 scence, parts which have been previously acted 

 upon by muscular contraction. John Hunter 



fully appreciated the value and utility of this 

 structure in supplying the place of muscle, with 

 less expense of exertion to the economy, and 

 assigned it a place in the arrangement of his 

 museum.* The thyro-hyoid and crico-thyroid 

 ligaments in man are formed of this struc- 

 ture. 



5. Synovial membrane. The articular syno- 

 vial membranes, (by the older anatomists called, 

 and confounded with, the capsular ligaments,) 

 like all others, possess in common with serous 

 membranes the form of a sac shut in all points; 

 they line the whole interior of the joints, and 

 secrete from their internal surface a peculiar 

 fluid, obviously destined for the lubrication of 

 the articular surfaces. These membranes are 

 remarkable for their great tenuity; they are 

 transparent ; in a state of inflammation, their 

 vascularity, which is imperceptible during 

 health, becomes very apparent by the general 

 redness which the membrane assumes; and 

 their internal or secreting surface is easily dis- 

 tinguished from the external, by contrasting the 

 smooth and glistening appearance of the former 

 with the roughness which the latter receives 

 from the cellular tissue and ligamentous fibres 

 which adhere to it. The internal surface of 

 the membrane is sometimes thrown into folds 

 with fringe-like margins, which project into 

 its cavity or sac. These folds contain more 

 or less of cellular tissue and a number of 

 pellets of fat, which being supplied with ves- 

 sels, the margin of the synovial fringe is some- 

 times tinged red. These folds are compared, 

 and certainly with much justice, to the epi- 

 ploic folds of the abdominal serous mem- 

 branes, more especially to the appendices 

 epiploica,' of the great intestine. Beclard sup- 

 poses that these fringes are specially the seat of 

 the synovial secretion, which being perspiratory 

 likewise takes place, though less abundantly 

 and manifestly, from the rest of the synovial 

 surface. The best examples of these folds 

 occur in the knee and hip-joints, in the former 

 of which they have been absurdly called alar 

 ligaments. 



Some idea may be formed of the manner in 

 which the synovial membrane is related to the 

 other articular structures by examining the an- 

 nexed figure, (fig. Ill,) representing a vertical 

 section of the knee-joint. The cut margin of 

 the synovial membrane is indicated by a, which 

 after lining the posterior surface of the patella 

 and ligamentum patellae, is reflected upon the 

 condyles of the femur, whence it is carried in 

 front of the crucial ligaments to line the arti- 

 cular surface of the head of the tibia, and from 

 that is again reflected upwards, and is con- 

 tinuous with the portion lining the posterior car- 

 tilaginous surface of the patella. This descrip- 

 tion is founded on the opinion, which I believe 

 to be correct, that the analogy between serous 

 and synovial membranes is accurate, in so far 

 as their possessing in common the form of 

 shut sacs is concerned. On this subject, how- 



' Vide Home's Lect. on Comp. Anat. Lect. i. 

 vol. i. 



