“Their (synovial) membrane differs from the synovial membrane of joints in not having so continuous or definite an endothelial lining; indeed, while some bursæ, such as that beneath the ligamentum patellæ, have a more or less regular lining of regular endothelium, 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. Bursæ 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. Bursæ underlying parts which have an extensive range of motion are _unilocular_, with a single cavity. Bursæ 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 bursæ are unilocular, most of the subcutaneous bursæ are multilocular.” [67] _Text Book of Human Anatomy._ A. Macalister, 1889, p. 48. 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 Bursæ Enumerated. The following is a list of bursæ 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 stemo-hyoid muscle. (D) One above the hyoid bone. _Pharynx._ A small central pit constituting a single bursa the _bursa pharyngea_. _Behind the angle of the lower jaw._ One. _On the symphysis of the chin._ One. _On the Acromion process._ One. _Beneath the deltoid_ and the acromion process, one large bursa often opening into the shoulder-joint. _Elbow._ (A) One over the olecranon. (B) One occasionally over the inner epicondyle. (C) One over the internal condyle of the humerus. (D) One over the external condyle of the humerus. (E) Small one between the biceps tendon and the head of the radius. (F) Often a second bursa which separates the tendon from the oblique ligament crossing it. _Wrist._ (A) One over the styloid process of the radius. (B) One over the styloid process of the ulna.