42 SECRETION. 



The arrangement of the synovial bursse is very simple. 

 Wherever a tendon plays over a bony surface, we find a 

 delicate membrane in the form of an irregularly shaped, 

 closed sac, one layer of which is attached to the tendon, and 

 the other to the bone. These sacs are lined with an epi- 

 thelium like that found in the synovial cavities, and they 

 secrete a true synovial fluid. Numerous bursse are also 

 found beneath the skin, especially in parts where the integu- 

 ment moves over bony prominences, as the olecranon, the 

 patella, and the tuberosities of the ischium. These sacs, 

 sometimes called bursse mucosse, are much more common in 

 man than in the inferior animals, and have essentially the 

 same function as the deep-seated bursse. The form of both 

 the superficial and deep-seated bursse is very irregular, and 

 their interior is frequently traversed by small bands of 

 fibrous tissue. The synovial sheaths, or vaginal processes, 

 line the canals in which the long tendons play, particularly 

 the tendons of the flexors and extensors of the fingers and 

 toes. They have essentially the same structure as the 

 bursse, and present two layers, one of which lines the canal, 

 while the other is reflected over the tendon. The vascular 

 folds, described in connection with the articular synovial 

 membranes, are found in many of the bursae and synovial 

 sheaths. 



Pericardial, Peritoneal, and Pleural Secretions. In 

 the normal condition of the true serous membranes, the 

 amount of secretion is very small ; so small, indeed, that it 

 never has been obtained in quantity sufficient for ultimate 

 analysis. It is not true that these membranes produce 

 merely a vaporous exhalation. Their secretion is always 

 liquid, and, small as it is in quantity, it can be found in the 

 pericardial sac, and sometimes in the lower part of the ab- 

 dominal cavity. As the only apparent function of these 

 fluids is to moisten the membranes, so that the opposing 

 surfaces can move over each other without undue fric- 



