180 INITIATIVE IN EVOLUTION 



bursse lie between exposed areas of skin and projecting bony 

 points, such as the patella, olecranon, ankles, etc. 



" Their (synovial) membrane differs from the synovial 

 membrane of joints in not having so continuous or definite 

 an endothelial lining ; indeed, while some bursse, such as that 

 beneath the ligamentum patellse, have a more or less regular 

 lining of regular endotheliun, others have only elongated 

 connective cells forming an imperfect lamella, and there are 

 all possible gradations met with between the regular saccular 

 bursa, and a loose meshwork of areolar tissue of which the 

 bursa is only a specialisation. Bursse may be (1) subcutaneous 

 (2) subfascial (3) between two tendons, or (4) between tendons 

 and subjacent ligaments or bone. Of these, some communicate 

 with the neighbouring joints always, some occasionally, and 

 some never. Bursse underlying parts which have an extensive 

 range of motion are unilocular, with a single cavity. Bursae 

 spread over an extensive surface, and whose walls move but 

 little on each other, are often divided by imperfect fibrous 

 septa, and are called multilocular. Almost all the lesser 

 bursse are unilocular, most of the subcutaneous bursse are 

 multilocular." 



Now if one were not engaged upon such a problem as that of 

 initiative in evolution and in trying to give examples of it there 

 would be no Gordian knot to cut, and the condensed statement 

 of Macalister might be simply taken as an accepted account of the 

 manner in which reading between the lines a bursa is formed in the 

 animal body. But, when an hypothesis such as the present is in 

 question, one may not cut the Gordian knot in this way, and must 

 produce briefly certain observations of the process, not only those 

 known in man by anatomists and surgeons but also some found in 

 lower Primates. 



Human Bursae Enumerated. 



The following is a list of bursse in man of which some are 

 normal or always present, and others which are both occasional 

 in their appearance and often imperfectly developed. 



Front of Neck. 



(a) One in front of the pomum adami. 



(b) One in the thyro-hyoid space extending to the under 

 surface of the hyoid bone. 



(c) One beneath the sterno-hyoid muscle. 



(d) One above the hyoid bone. 



