296 SPECIAL HISTOLOGY. 



membranes, distinct from the fibrous capsules, as they are termed, 

 which possess in all respects the structure of fibrous ligaments, consist : 

 1, of a layer of connective tissue, with not very numerous vessels and 

 nerves ; and, 2, of an epithelium. The latter is composed of from one 

 to four layers of large tessellated cells, measuring 0-005 0*008 of a 

 line, with roundish nuclei of 0'002-0'003 of a line. The former, in its 

 innermost part, is constituted of a layer of parallel fasciculi, with indis- 

 tinct fibrils and elongated nuclei or fine elastic filaments ; more exter- 

 nally of decussating bundles, with a fine elastic network, occasionally 

 also of a network of bundles of connective tissue of very various thick- 

 ness, with winding elastic fibres, exactly as in the arachnoid. Not 

 unfrequently, common fat-cells occur, dispersed here and there in the 

 meshes of the connective tissue, although upon the whole very rarely ; 

 and also a few scattered cartilage-cells, with tolerably thick, opaque 

 walls, and a distinct nucleus. The synovia! membranes possess neither 

 glands nor papillae, whilst they present large adipose masses (plicce adi- 

 posce) and vascular processes (plicce vasculosce, plicce synoviales, liga- 

 menta mucosa, of authors). The former, at one time erroneously termed 

 "Haversian glands," are found principally in the hip- and knee-joints, 

 in the form of yellow or yellowish-red soft processes or folds, and con- 

 sist simply of large collections of fat-cells in vascular portions of the 

 synovial membrane. The latter are met with in almost every joint, 

 constituting, provided that the blood-vessels are filled, red, flattened 

 projections of the synovial membrane, with an indented and plicated 

 margin, and furnished with minute processes. These folds are usually 

 placed close to the junction of the synovial membrane with the carti- 

 lage, upon which they lie flat, thus forming, in many cases, a sort of 

 coronal around it ; in others they are more isolated, and placed in other 

 parts of the articulation. In their structure, they differ from the rest 

 of the synovial membrane principally in their great vascularity, con- 

 sisting as they do of little else than minute arteries and veins, and 

 delicate capillaries forming wavy loops at the edge of the processes, and 

 consequently they are very similar to the choroid plexuses in the ven- 

 tricles of the brain. Besides the vessels, they present a matrix of, 

 frequently, distinctly fibrous, connective tissue, the usual epithelium of 

 the synovial membrane, occasionally solitary or numerous fat-cells, and, 

 more rarely, isolated cartilage-cells. At the edge, they are almost 

 invariably furnished with minute, foliated, conical, membranous pro- 

 cesses of the most extraordinary forms (often resembling the stems of a 

 cactus), which also frequently contain vessels, but are for the most part 

 constituted merely of an axis of indistinctly fibrous connective tissue, 

 with occasional cartilage-cells, and an epithelium, very thick in places. 

 The smaller ones frequently consist even of nothing but epithelium, 

 or of little else than connective tissue. 



