48 CONNECTIVE TISSUES. 



as sharply defined threads which run an isolated course, some- 

 times straight, sometimes contorted, or even spiral. By repeated 

 bifurcations and fusions of the branches again with one another, 

 they form a network. These facts may be demonstrated very 

 advantageously in a serous membrane, particularly in the meso- 

 colon of the rabbit, or in that part of the parietal peritoneum 

 of the sanfti animal which lies on either side of the lumbar ver- 

 tebrae. In both of these situations the elastic fibres are very 

 strongly developed. If preparations of these or similar mem- 

 branes are treated with acetic acid, the bundles of common 

 connective tissue disappear, so that the network of elastic 

 fibres becomes prominent. 



To show the elastic fibres of the ligamenlum nuclise, the best 

 way is to make preparations by teasing a portion of that of 

 the ox, in salt solution, either in the fresh condition, or after 

 maceration for a day or more in sherry-colored solution of 

 bichromate of potash. In either case we have before us thick, 

 solid, shiny cords of homogeneous substance, which branch 

 dichotomously, uniting by their branches so as to form a net- 

 work. The individual fibres, however, run mostly in one direc- 

 tion, and are so close to one another, that, on superficial exami- 

 nation, they exhibit the appearance of a reticular arrangement. 

 Such fibres as happen to be separated from the rest are often 

 rolled up like a watch-spring. 



The dichotomously-branching elastic fibres of the pulmonary 

 substance can be shown, either by teasing fragments of fresh 

 lung (an operation which requires an immense deal of patience), 

 or in sections of fresh lung hardened by freezing, as will be 

 afterwards described. The elastic so-called fenestrated mem- 

 branes which exist in the tunica intima of the large arteries 

 may be demonstrated as follows: A part of the aorta of a rab- 

 bit or guineapig, having been cut out, is pinned down on a flat 

 cork with the internal surface upwards. The membrane having 

 been fixed at a certain point with a needle, the intima is raised 

 up close to the latter with sharp forceps, and then shreds as 

 long as possible are stripped off a process which requires no 

 remarkable skill. Any one possessed of the requisite dexterity 

 may then strip off thin lamellae from the deep surface of these 

 shreds ; these may be at once mounted, and are so thin that 

 the fenestrated membrane can be seen at the edges without 

 further preparation. If this does not succeed, the student 

 must content himself with teasing out the shreds first obtained. 



Finally, a network of elastic fibres can be shown very beauti- 

 fully in the vocal cords of the frog. To any one who is suffi- 

 ciently acquainted with the general anatomical relations of the 

 parts, it is not difficult to remove those structures even from 

 the living animal. The easiest way is to place the vocal cord 

 for a few minutes in dilute acetic acid, and then to scrape off 



