CELLULAE ELEMENTS OF THE GROUND-SUBSTANCE. 21 



were distinctly situated in the lymph-canalicular system, whereas in the 

 central parts the branched cells were transformed into a delicate 

 eticulum of cells, the bodies of which had become considerably 

 smaller, and the processes very thin and delicate. The meshes were 

 filled out nearly completely by lymphoid corpuscles ; and there was 

 nothing to be seen of an intercellular matrix. 



After what has been said about the distribution of those nodules 

 and tracts it is scarcely necessary to draw the special attention of the 

 reader to the fact that from their topographical arrangement they 

 are analogues of the fat tissue of the omentum. We will, therefore, 

 consider in the following paragraph the structure and the develop- 

 ment of the fat tissue in so far as it is necessary to show the very 

 intimate relation between the above-mentioned perilymphangial 

 structures and the fat tissue of the omentum. Before doing so we 

 will describe first an organ which is situated in the fossa infra- 

 orbitalis of young rabbits and guinea-pigs, the structure of which is 

 able to throw some light on our discussion about the relation of the 

 fat tissue and the perilymphangial structures. 



By the side of the glandula infra-orbitalis lies a mass of fat, 

 which appears sometimes to be more or less isolated from the gland 

 as a separate structure, and sometimes to represent only an envelope 

 of that gland. In young and half-grown animals it is generally 

 found to consist for the most part of a perfectly hyaline matrix, and 

 to contain only a few small fat lobules. The older the animal gets 

 the more fat lobules and the less hyaline substance are to be found 

 in it. 



The best method of preparing this structure for examination is the 

 following : the skin and subcutaneous tissue are first removed, and 

 the fascia which bridges over the fossa of the infra-orbital gland is then 

 slit up. A small portion of the hyaline body, which now protrudes 

 through the opening, can be snipped off with fine curved scissors, and 

 mounted in aqueous humor. The following appearances will then be 

 found under the microscope : in some places, there are a very few thin, 

 isolated, wavy, shining connective tissue bundles, with here and there 

 an amoeboid corpuscle ; in other portions very little is to be seen in 

 the perfectly hyaline matrix, while elsewhere the matrix contains a 



