MINUTE ANATOMY OF THE OMENTUM. 239 



nuclei. The presence of two nuclei in one endothelial cell 

 was, however, seldom met with in the omentum of rat. 



The presence of smaller or larger groups of germinating 

 endothelial cells occurring in various parts of the normal 

 omentum and pleura of various animals, fully described and 

 figured in the above-mentioned book, need not here be 

 mentioned specially. 



2. According to Rollet the fenestrse of the omentum are 

 surrounded by connective-tissue bundles, which return in 

 themselves, and judging from his fig. 3 in his article on con- 

 nective tissue, one is led to suppose that in the omentum 

 there are no other bundles but such as surround the fenestrae 

 and return in themselves. Ranvier ('Travaux de laboratoire 

 d'Histologie,' 1874, p. 140) questions this statement, and 

 maintains on the contrary that there are no bundles return- 

 ing in themselves, and that the fenestrse originate by the 

 simple separation of bundles, i. e. are merely holes between 

 bundles. Ranvier thinks it probable that the holes are pro- 

 duced by migratory cells penetrating through the membrane. 



Examining the omentum of young rabbits and guinea pigs, 

 prepared in the above manner, the origin of the fenestrse 

 becomes easily understood ; the examination of the omentum 

 of rats and half-grown dogs gives us also valuable informa- 

 tion as regards the arrangement of the connective-tissue 

 bundles in the fenestrated part. There is a considerable 

 part of the omentum of young guinea pigs (three to four 

 weeks old), and still more, of young and even full-grown 

 rabbits, which is of a dense structure, containing only here 

 and there a few small holes. The omentum of guinea pigs 

 (three to four weeks old) is especially valuable in this 

 respect, showing us at once the origin of the holes. In fig. 

 vii I have represented a small portion of such an omentum. 

 As is shown in the figure, the membrane consists of connec- 

 tive-tissue bundles, arranged more or less parallel to each 

 other ; on the surface of the membrane are seen the nuclei 

 of the endothelium (the outlines of the endothelial cells 

 becoming of course visible by nitrate of silver). Further, 

 we see a number.of well-defined holes, a, passing right through 

 the membrane, these holes being of diflferent sizes. And 

 finally, we notice in the membrane a number of round 

 spaces (vacuoles) of different sizes — in some parts their num- 

 ber being very considerable; some of them contain a small 

 nucleus, i. e. the nucleus of a connective-tissue cell, the 

 substance of which may be made out occasionallly as granular 

 protoplasm situated at and extending from the poles of the 



