66 GENERAL ANATOMY OF THE TISSUES. 



hand in young animals, in which also Virchow made his first 

 observations, and especially in embryos, it is easy to come to a 

 clear decision upon the matter. In man, I find the tendons, 

 ligaments, and the aponeurosis palmaris and plantaris, to be 

 especially serviceable objects ; but in all the places in which 

 elastic tissue is mixed with connective tissue, I was able to 

 follow their development. The observation is most successful 

 in the foetus of three to four months. Here, in all the more 

 solid organs composed of connective tissue, — tendons, ligaments, 

 fascise, corium, — the proper connective-tissue fibrils are already 

 quite well developed, while of nuclear fibres, so to speak, there 

 are no traces. Instead of these, however, we find between the 

 often very distinct bundles of connective tissue, a great number 

 of fusiform cells of 0-01'" — -015"' in length, which in their 

 middle (of , 002" / — 0-003'" in breadth) inclose an elongated 

 roundish clear nucleus with a nucleolus, which completely fills 

 them, and are prolonged at their ends into fine dark threads. 

 If we trace these cells, among which are always scattered many 

 round and elongated cells out of which they are formed, and in 

 older embryos a few stellate ones, with from 3 to 5 processes, 

 it is found that they gradually become longer and narrower, 

 and from the sixth month begin to coalesce with one another 

 into elongated fibres or networks ; up to a late period, however 

 (even 7 to 8 months), these formative cells of the elastic tissue 

 maybe easily isolated in abundance from all forms of connective 

 tissue, either singly or combined by twos and threes. In the 

 foetus at birth this can no longer be done ; but here the 

 complete nucleus fibres, at least in the more solid forms of 

 connective tissue, still clearly exhibit their composition out 

 of fusiform and stellate cells with nuclei; which, as we have 

 already seen, is occasionally in some localities even the case 

 in the adult. 



What holds good of the nucleus fibres may be asserted also 

 of the elastic fibres, which are not further treated of by 

 Donders and Virchow. Valentin (Wagner's ' Handw. d. 

 Phys./ I, p. 668) found that the elastic fibres of the Ug amentum 

 nucha of the calf are considerably finer than those of the ox, 

 and I stated ('Zeitschrift fiir Wiss. Zool./ I, p. 77, Anm.) that 

 all the thick elastic fibres of the adult have at one time been 

 common nucleus-fibres. In fact, we find in the new-born 



