BURS^. 



Ill 



the capsules separating two distinct joints which have broken down so as to make a 

 common articular cavity. Such ligaments retain their synovial covering and really 

 lie without the joint-cavity. 



Vessels and Nerves. — Important arterial anastomoses surround all the larger 

 joints ; from the larger vessels small branches pass inward to the ends of the bones, 

 to the periphery of the articular cartilages, and to the capsule. The margins of the 

 cartilages are surrounded by vascular loops ; the articulating surfaces are, however, 

 free from blood-vessels. The synovial membrane is usually well supplied with 

 minute branches, a rich net-work being described at the bases of the synovial fringes. 

 The veins form strong plexuses. 



Lymphatics are found well developed directly beneath the inner surface of the 

 synovial membrane ; while it is certain that they absorb from the joint, direct open- 

 ings into the articular cavity have not been demonstrated. 



Nerves, presumably sensory and vasomotor, end in the tissues around the syno- 

 vial membrane. In addition to the Pacinian bodies, which are sometimes very 

 numerous, Krause has described special articular end-bulbs outside the synovial 

 membrane surrounding the finger-joints in man. 



Fig. 137. 



•-:x~>^ 



Blood-vessel 



Free surface of — 

 articular car- 

 tilage 



Bone 



Marrow-cavity 



 v j,j 'Synovial mem- 



'Union of carti- 

 lage and syno- 

 vial membrane 



Section through margin ot joint, showing articular cartilage and capsule. X 135. 



Bursae ' are sacs filled with fluid found in various places where friction occurs 

 between different layers or structures. They are sometimes divided into synovial 

 and fuucoiis bursae. These varieties are distinct in typical instances, but, since the 

 one passes insensibly into the other, it is doubtful whether this subdivision is war- 

 ranted. Some bursae, especially those around the tendons of the fingers, have a 

 true synovial lining reflected over the tendons, and are surrounded by strong fibrous 

 sheaths known as the thecce synoviales. ^ Other bursae are placed as capsules around 

 a cartilage-coated facet over which a tendon plays. Both the vaginal and capsular 

 varieties may be classed as synovial bursae. Representatives of the mucous bursae 

 are those within the subcutaneous tissue where the skin is exposed to friction, as at 

 the elbow and the knee. These bursae seem little more than exaggerations of the 

 spaces between layers of areolar tissue. The same may be said of some of those 

 among the muscles. The mucous bursat are provided with more or less of a cellu- 

 lar lining, but the latter is less perfect than in the synovial class. A bursa may be 

 simple or composed of several cavities communicating more or less freely. They 

 often communicate with joints. Their number is uncertain. "Many, perhaps most, 

 are present at birth, but new ones may appear in situations exposed in certain 



' Bursae synoviales. "Vaginae mucosae tendinum. 



