ARTHROLOGY 281 



Synovial Membranes. — These membranes are so named because 

 they secrete a fluid, viscid Hke white of egg, which is called synovia. 

 They serve to diminish friction and so facilitate movement Their 

 situations are therefore associated with movable structures, such as 

 joints, gliding tendons, and the integument over bony projections. 

 Accordingly there are three kinds of synovial membrane — namely, 

 articular, tendon or vaginal, and bursal. 



The articular synovial membranes line the interior of diarthrodial 

 joints, except where there is articular cartilage, and they stop at 

 the margin of this cartilage. In some joints they give rise to folds, 

 some of which contain adipose tissue. Such folds are known as 

 Haversian mucilaginous glands. 



The tendon or vaginal synovial membranes, also known as synovial 

 sheaths, invest those tendons which have to glide within fibrous 

 sheaths. They are met with around the ankle, particularly behind 

 the external and internal malleoli, and upon the palmar aspect of 

 the fingers. 



The bursal synovial membranes, commonly caUed synovial 

 bursae, are synovial sacs which are situated between the integument 

 or a muscle and some bony projection. They may be deep- 

 seated or subcutaneous. The deep-seated burscB are situated between 

 a muscle, or its tendon, and the contiguous bone,— e.g., the tendon 

 of the biceps brachii and the anterior part of the bicipital tuberosity 

 of the radius. The subcutaneous hurscB are placed beneath the in- 

 tegument, which they separate from some bony projection — e.g., 

 the prepatellar bursa. 



Stractare. — A synovial membrane consists of connective tissue, which is 

 destitute of an endothelial Uning properly so called. At intervals it may pre- 

 sent scattered groups of branched cells, but these are not endothelial. There 

 are many capillary bloodvessels, and lymphatic vessels are described as being 

 present. The nerves are described as terminating in corpuscles of the nature 

 of end-balls, in a plexiform manner, and in Pacinian corpuscles. 



Development. — Synovial membranes are developed from the axial 

 mesenchyme of the limb-buds, in the intervals between contiguous bones, 

 which are being formed from that mesenchyme. 



Interarticular Fibro-carMlages. — These are met with in certain 

 joints either in the form of plates separating the articular ends, or 

 as bands placed around cavities, which they serve to deepen, or 

 around fiat surfaces, which they render concave. They are known 

 as menisci. When the fibro-cartilage takes the form of a plate it 

 is spoken of as an interarticular meniscus. Such occur at the 

 temporo-mandibular, stemo-clavicular, and radio-carpal joints. 

 They act as buffers to break shock, and they compensate for 

 .rregularities of the opposed surfaces. When the fibro-cartilage is 

 iimited to the margin of a cavity, or the circumference of a surface, 

 it is called a marginal meniscus, such as the glenoid ligament of 

 the shoulder-joint, the cotyloid hgament of the hip-joint, and the 

 [Semilunar fibro-cartilages of the kjiee-joint. 



Movements.— The different kinds of movement at diarthrodial 

 oints are angular, circumduction, rotation, and gliding. 



