86 GENERAL ANATOMY OF THE TISSUES. 



quite well developed, while of nuclear fibres, so to speak, there are no 

 traces. Instead of these, however, we find between the often very dis- 

 tinct bundles of connective tissue, a great number of fusiform cells of 

 O01--015 of a line in length, which in their middle (of 0-002-0-003 

 of a line in breadth) enclose 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 may be 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 connec- 

 tive tissue, still clearly exhibit their composition out of fusiform and 

 stellate cells with nuclei ; which, as we have already seen, is occasion- 

 ally 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 ligamentum nuchce of the calf are considerably finer than 

 those of the ox, and I stated (" Zeitschrift fur Wiss. Zool.,"L p. 77, Anm.) 

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

 mon nucleus-fibres. In fact, we find in the new-born child not a single 

 true elastic fibre, since even those of the ligt. nuchce, of the ligt. flava, 

 and of the aorta, when largest, do not measure more than 0-0008--001 

 of a line. This circumstance alone, might, if we take into account the 

 close resemblance of the elastic and so-called nucleus-fibres in other 

 respects, be considered as a demonstration that the former are also 

 developed out of cells, but we have in addition direct evidence that 

 this is their mode of development 



In the aorta, in the ligt. nuchce, and in the fascia superficialis abdo- 

 minis of human embryos of the fourth and fifth months, we find the 

 same short fusiform cells as in the common connective tissue ; and 

 their coalescence into originally finer fibres, though perhaps not quite 

 so readily demonstrable as in the former localities, may yet be made 

 out with certainty, so that the agreement in their genesis of the finer 

 with the coarser elastic fibres, may be considered to be established. 



Not, however, to the same extent, as with regard to the genesis of 

 the finer elastic fibres, can I agree with the authors mentioned in other 

 points. In the first place, concerning the physiological import of the 

 so-called nucleus-fibres, I grant to Virchow, that even in the adult, 



