184 ARTICULATIONS. 



in the knee, and the tendon of the Biceps in the shoulder. In most of the joints, 

 the synovial membrane is thrown into folds, which project into the cavity. 

 Some of these folds contain large masses of fat. These are especially distinct in 

 the hip and the knee. Others are flattened folds, subdivided at their margins into 

 fringe-like processes, the vessels of which have a convoluted arrangement. The 

 latter generally project from the synovial membrane near the margin of the 

 cartilage, and lie flat upon its surface. They consist of connective tissue, covered 

 with epithelium, and contain fat cells in variable quantity, and, more rarely, 

 isolated cartilage cells. They are found in most of the bursal and vaginal, as 

 well as in the articular synovial membranes, and were described, by Clopton 

 Havers, as mucilaginous glands, and as the source of the synovial secretion. 

 Under certain diseased conditions, similar processes are found covering the entire 

 surface of the synovial membrane, forming a mass of pedunculated fibre-fatty 

 growths, which project into the joint. 



The bursse are found interposed between surfaces which move upon each other, 

 producing friction, as in the gliding of a tendon, or of the integument over pro- 

 jecting bony surfaces. ' '"They admit of subdivision into two kinds, the bursse 

 mucosse and the synovial bursse. The former are large, simple, or irregular 

 cavities in the subcutaneous areolar tissue, inclosing a clear viscid fluid. They 

 are found in various situations, as between the integument and front of the patella, 

 over the olecranon, the malleoli, and other prominent parts. The synovial bursse 

 are found interposed between muscles or tendons as they play over projecting 

 bony surfaces, as between the Glutei muscles and surface of the great trochanter. 

 They consist of a thin wall of connective tissue, partially covered by epithelium, 

 and contain a viscid fluid. Where one of these exists in the neighborhood of a 

 joint, it usually communicates with its cavity, as is generally the case with the 

 bursa between the tendon of the Psoas and Iliacus, and the capsular ligament of 

 the hip, or the one interposed between the under surface of the Subscapularis and 

 the neck of the scapula. 



The vaginal synovial membranes or synovial sheaths serve to facilitate the 

 gliding of tendons in the osseo-fibrous canals through which they pass. 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 outer surface of the con- 

 tained tendon ; the space between the two free surfaces of the membrane being 

 partially filled with 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 osseo-fibrous canals in the hand or foot. 



Synovia is a transparent, yellowish- white, or slightly reddish fluid, viscid like 

 the white of egg, having an alkaline reaction, and slightly saline taste. It consists, 

 according to Frerichs, in the ox, of 94.85 water, 0.56 mucus and epithelium, 0.07 

 fat, 3.51 albumen and extractive matter, and 0.99 salts. 



The Articulations are divided into three classes: Synarthrosis, or immovable 

 joints; Amphiarthrosis, or mixed joints; and Diarthrosis, or movable joints. 



1. SYNARTHROSIS. IMMOVABLE ARTICULATIONS. 



Synarthroses (ovv, with, apOpov, a joint) or Immovable Joints include all those 

 articulations in which the surfaces of the bones are in almost direct contact, not 

 separated by an intervening synovial cavity, and immovably connected with 

 each other, as between the bones of the cranium and face, excepting the lower 

 jaw. The varieties of synarthrosis are three in number ; Sutura, Schindylesis, 

 and Gomphosis. 



Sutura (a seam). Where the articulating surfaces are connected by a series of 

 processes and indentations interlocked together, it is termed sutura vera ; of which 

 there are three varieties, sutura dentata, sutura serrata and sutura limbosa. The 

 surfaces of the bones are not in direct contact, being separated by a layer of mem- 

 brane continuous externally with the pericranium, internally with the dura mater. 



