126 ELASTIC TISSUE. 
state that a transition of these cells into elastic tissue was 
proved by observation. If, however, such be really the process 
of formation, as, from analogy, we are entitled to suppose, 
the bodies of these cells must then take a much more important 
share in the formation of the fibres than those of areolar tissue 
do, and the formation of the elastic fibres of the aorta holds a 
middle position between the generation of the horny fibres in 
the cortical substance of feathers (see p. 86, and pl. II, fig. 13) 
and the production of fibres in areolar and fibrous tissues. 
The reticular appearance of elastic tissue loses its singularity, 
when it is conceived to be generated in the same manner 
as those horny fibres in the feather, that is, partly by’ 
an elongation of the cells, and partly by a splitting of 
their bodies. The splitting of the elastic fibres is not to 
be regarded as an isolated phenomenon, since such division 
undoubtedly occurs in transitional stages in the development 
of all forms of areolar and fibrous tissue in the foetus. 
In this respect the elastic tissue seems to remain at a lower 
stage of development. Purkinje and Raiischel observed a 
darkish point in the centre of a transverse section of the 
elastic fibres of the aorta, and a dotted line m the course of 
the fibres, and thence inferred the existence of a rudimentary 
canal in their interior. This supposition, which I must 
confess formerly struck me as being a very bold one, has 
much more weight now, inasmuch as it is not improbable 
that all fibres which are formed by the prolongations of 
cells (even those of areolar tissue) are hollow, at least, that 
they are not composed throughout of one uniformly solid 
mass. If, as an observation of Valentin’s seems to indicate, 
still more minute fibres may be rendered visible by the aid 
of caustic potash in those of ordinary elastic tissue, I 
should be inclined to regard them as analogous to the primi- 
tive muscular fibres, whose signification, as we shall subse- 
quently see, differs entirely, in a morphological view, from the 
primitive fibres of areolar tissue. 
Whilst the elastic tissue of the aorta taken from a very 
young foetal pig exhibited in the manner before described the 
main characteristics of the tissue, namely, its yellowish colour 
and elasticity, the ligamentum nuche of a sheep’s foetus, at a 
much later period of gestation, was but very slightly developed. 
eS ee aes 
