262 



THE ARTICULATIONS, OR JOINTS 



be continued over the surface of the cartilages; but in the adult it merely encroaches for a short 

 distance upon the margins of the cartilages, to which it is firmly attached; it then invests the 

 inner surface of the capsular or other ligaments enclosing the joint, and is reflected over the 

 surface of any tendons passing through its cavity, as the tendons of the Popliteus in the knee 

 and the tendon of the Biceps in the shoulder. In some of the joints the synovial membrane 

 is thrown into folds, which pass across the cavity. They are called synovial ligaments, 

 and are especially distinct in the knee. These folds, when large, frequently contain con- 

 siderable quantities of fat, which acts as a cushion between the two articular surfaces and 

 serves a valuable purpose in filling up gaps. In some joints there are flattened folds, sub- 

 divided at their margins into fringe-like processes (synovial villi), the vessels of which have 

 a convoluted arrangement. These latter generally project from the synovial membrane near 

 the margin of the cartilage and lie flat upon its surface. They consist of fibroelastic tissue 

 covered with endothelium, and contain fat-cells in variable quantities, and, more rarely, isolated 

 cartilage-cells. Under certain diseased conditions similar processes are found covering the 

 entire surface of the synovial membrane, forming a mass of pedunculated fibrofatty growths 

 which project into the joint. Similar structures are also found in some of the bursal and vaginal 

 synovial membranes. 



The bursal synovial membranes are sacs interposed between surfaces which move upon each 

 other, producing friction, as in the gliding of a tendon or of the integument over projecting bony 

 surfaces. There are two groups of synovial bursae designated according to situation: (1) Sub- 

 cutaneous synovial bursaa {bursae mucosae subcutaneae) (Fig. 214) are those situated between the 

 integument and a prominent process of bone. Subcutaneous bursae are found between the 

 integument and the front of the patella, over the olecranon, the malleoli, and other prominent 

 parts. (2) Subtendinous synovial bursae (bursae mucosae subtendineae) (Fig. 214) are those situ- 

 ated between tendons or muscles and the bony or cartilaginous surfaces over which the tendons 

 or muscles glide. For example, a bursa is placed between the Glutei muscles and the surface 



FIG. 214. Scheme of a serous bursa. (Poirier and Charpy.) 



of the great trochanter. Subtendinous bursse are found often about joints and not unusually com- 

 municate directly with the cavity of the joint by means of an opening in the joint capsule, the 

 synovial membrane of the joint being continuous with the synovial membrane of the bursa. 

 For instance, the bursa between the tendon of the Psoas and Iliacus muscles and the capsular 

 ligament of the hip communicates with the hip-joint; and the bursa between the under surface 

 of the Subscapularis muscle and the neck of the scapula communicates with the shoulder-joint. 

 Bursse consist of a thin wall of connective tissue, lined by endothelial cells, and contain a viscid 

 fluid. 



The vaginal synovial membrane (Figs. 257 and 365), which is the synovial sheath or the 

 thecal synovial bursa (vagina mucosa tendinis], serves to facilitate the gliding of a tendon in the 

 osseofibrous canal through which it passes. The membrane is here arranged in the form of 

 a sheath, one layer of which adheres to the wall of the canal, and the other is reflected upon the 

 surface of the contained tendon, the space between the two surfaces of the membrane containing 

 synovia. These sheaths are chiefly found surrounding the tendons of the Flexor and Extensor 

 muscles of the fingers and toes as they pass through the osseofibrous canals in the hand or foot. 

 A vaginal sheath covers the long head of the Biceps brachii muscle from its origin to the surgical 

 neck of the humerus (Fig. 247). 



Subjacent to the synovial membrane of certain joints are found pads of adipose tissue, the 

 synovial pads. These serve to fill up large spaces, and by adapting themselves to changes of 

 position maintain the form of the joint during movement. 



