cxciv SYXOVIAL MEMBRANES. 



line and by their synovial secretion lubricate the cavities of the diar- 

 throdial articulations, that is, those articulations in which the opposed 

 surfaces glide on each other. In these cases the membrane may be 

 readily seen covering internally the surface of the capsular or other 

 ligaments which bound the cavity of the joint, and affording also an 

 investment to the tendons or ligaments which happen to pass through 

 the articular cavity, as in the instance of the long tendon of the 

 biceps muscle in the shoulder-joint. On approaching the articular 

 cartilages the membrane passes over their margins, and, becoming much 

 more firmly adherent, terminates after advancing hut a litrle way on their 

 surface. This, as already explained (page Ixxxiii. ), is the condition in the 

 adult ; but in the foetus the membrane, closely adhering, is continued over 

 the whole surface of the cartilage, so that it would seem to become oblite- 

 rated or absorbed in consequence of pressure or friction when the joint 

 comes to be exercised. The blood-vessels in and immediately underneath the 

 membrane are sufficiently manifest in most parts of the joint. They advance 

 but a little way upon the cartilages, forming a vascular zone round the 

 margin of each, named " circulus articuli vasculosus," in which they end by 

 loops of vessels dilated at the bent part greatly beyond the diameter of 

 ordinary capillaries. In the fostua, according to Mr. Toynbee, these 

 vessels, like the membrane itself, advance further upon the surface of the 

 cartilage. 



In several of the joints, folds of the synovial membrane, often containing more or 

 less fat, pass across the cavity ; these have been called synovial or mucous ligaments. 

 Other processes of the membrane simply project into the cavity at various points. 

 These are very generally cleft into fringes at their free border, upon which their blood- 

 vessels, which are numerous, are densely distributed. They often contain fat, and 

 then, when of tolerable size, are sufficiently obvious ; but many of them are very small 

 and inconspicuous. The fringed vascular folds of the synovial membrane were 

 described, by Dr. Clopton Havers (1691), under the name of the mucilaginous glands, 

 and he regarded them as an apparatus for secreting synovia. Subsequent anatomists, 

 while admitting that, as so many extensions of the secreting membrane, these folds 

 must contribute to increase the secretion, have, for the rno.st part, denied them the 

 special character of glands, considering them rather in the light of a mechanical pro- 

 vision for occupying spaces which would otherwise be left void in the motion of the 

 joints, and this view is no doubt right as regards the larger, fat-inclosing folds. 

 The smaller and less obvious fringes have, however, been found, on investigation by 

 Mr. Rainey, to be most probably secreting organs as originally supposed by Havers. 

 Mr. Rainey* has found that the processes in question exist in the bursal and vaginal 

 synovial membranes as well as in those of joints, wherever, in short, synovia is secreted. 

 He states that their blood-vessels have a peculiar convoluted arrangement, differing 

 from that of the vessels of fat, and that the epithelium covering them, "besides in- 

 closing separately each packet of convoluted vessels, sends off from each tubular sheath 

 secondary processes of various shapes, into which no blood-vessels enter." Kb'lliker, 

 who has since taken up the inquiry, also finds that fringed membranes exist in all 

 joints and synovial sheaths, as well as in most synovial bursse, and that they consist 

 of vascular tufts of the synovial membrane, covered by epithelium, and now and then 

 containing fat-cells and more rarely isolated cartilage cells. He also observed the 

 curious " non-vascular secondary processes," described by Mr. Rainey, the larger of 

 which, he says, consist of fibres of areolar tissue in the centre, sometimes containing 

 cartilage-cells, and a covering of irregularly thickened epithelium. 



2. Vesicular or Bursal synovial membranes, Synovial bursce, Bursce mucosce. 

 In these the membrane has the form of a simple sac, interposed, so as to 

 prevent friction, between two surfaces which move upon each other. The sy- 



* Proceedings of the Royal Society, May 7th, 1846. 



