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 pi. 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 Rauschel observed a 

 darkish point in the centre of a transverse section of the 

 elastic fibres of the aorta, and a dotted line in 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 nucha? of a sheep's foetus, at a 

 much later period of gestation, was but very slightly developed. 



