of Animal Bodies. 307 



there is reason to believe, that the blood from which the mate- 

 rials for secretion are derived does not directly reach the parietes 

 of the cul de sac, but only circulates in the interposed cellular 

 membrane. In other glands, again, and the lungs present a 

 striking example of this arrangement, the blood circulates in the 

 parietes of the extreme ducts, which are, in the case of the 

 lungs, the air-cells. I have already mentioned, that no elemen- 

 tary cylinders can be detected in certain tissues. It is very re- 

 markable that this is the case with respect to the air-cells of the 

 lungs, whose tissue, consequently, does not consist of condensed 

 cellular tissue, or, as I once thought, and as Magendie supposed, 

 of serous membrane. With respect to the bones of man and 

 animals, the observations of Treviranus fully establish the exist- 

 ence of the laminated structure. The laminae are arranged 

 into several layers. In the bones of man these layers are folded 

 and multifariously perforated, which is not the case in other ani- 

 mals. These folds in the lamina?, or their layers in the human 

 bones, appear in the longitudinal section to resemble fibres, for 

 which, when examined with a microscope, they are indeed easily 

 mistaken, and the perforations in the laminae produce an appear- 

 ance of cells. The perforations are entirely distinct from the 

 cavities or interstices discovered in the substance of human bones 

 by the microscope, and which are found in consequence of the 

 laminae not lying in complete apposition with each other, for 

 they leave between them interstices that are filled with fluid. 

 The researches of Treviranus, Deutsch, and Purkinje, have 

 completely established the foliated structure of bones, and have 

 also explained the circumstances which misled Scarpa, and in- 

 duced him to form the opinion that the osseous texture is cellu- 

 lar. To conclude, it is necessary to observe, that Treviranus 

 himself allows he has been anticipated in some of his investiga- 

 tions by the celebrated Ehrenberg, who has applied his practised 

 powers of microscopical observation to similar researches. Tre- 

 viranus, however, differs from Ehrenberg in several very import- 

 ant particulars, and has likewise pointed out the sources of 

 Ehrenberg's errors. 



