664 
PROFESSOR WILLIAMSON ON THE STRUCTURE AND 
portion of the section (fig. 23 ), from which point they proceed in divergent lines 
towards its inferior border. As the horizontal fibres of each lamina approach the line 
23 d, they gradually lose their parallelism, and unite to form bundles of various 
thicknesses ; owing to the manner in which the fibres forming each bundle redistribute 
themselves and contribute to the formation of other divergent bundles, there is pro- 
duced a curious reticular structure with oval or fusiform meshes. On examining the 
upturned extremities of the lamina?, we discover the same tissues, only in a modified 
form which exhibits great beauty, whether viewed in reference to its adaptation to 
the primary purpose of strengthening the organism, or to the exquisite appearance of 
the interlaced fibres. Fig. 24 , Plate XXX,, represents a vertical section made almost 
parallel with the outer margin, but with sufficient obliquity to cause it to traverse 
three of the vertical lamince at a very acute angle. Fig. 24 a is the superficial tissue 
(kosmine), and h the subjacent horizontal canals, divided nearly at right angles to 
their course ; c are the lower or horizontal portions of several laminae ; d, d represent 
the three vertical laminae, each consisting of an elaborate network of interlacing 
fibres ; the latter being continuations of those which form the parallel horizontal series 
in the horizontal portions of the laminae, and which have been already shown to 
assume a reticular arrangement as they approached the line fig. 23 d. Here this 
alteration in their distribution has attained its climax. The structure is not produced 
like those woven fabrics, where a warp and a weft interlace one another in opposite 
directions ; the fibres, originally spread out on one plane like the threads of a warp, 
are looped up into bundles at one point, only to be separated again and redistributed 
at another, when the individual fibres enter into the composition of new and divergent 
bundles, the interlacings of which leave numerous small meshes between them*. 
These tissues appear to be more dense and strong towards the outer, than at the 
inner surface of each lamina. 
The meshes thus left are occupied by bundles of the second series of fibres, which 
pass through them at right angles. Corresponding' with those which radiate from 
the centre of the section (fig. 23 ), and traverse the horizontal laminse, they are still 
more fully developed in the upturned vertical portions of each layer. Though the 
fibres are aggregated into large and strong bundles, they do not interlace so as to 
form a network ; all the fibres which enter into the composition of one fasciculus, 
continue to do so; and even the separate bundles retain their parallelism with each 
other. Fig. 25 represents a portion of one fasciculus, from which it will be seen, 
that whilst it is flattened out at intervals (25 a), the intervening parts are cylin- 
drical (25 h). The bundles of fibres, thus constructed, proceed horizontally from the 
centre to the circumference of the scale, following the direction of the canals in 
fig. 21 . Fig. 26 represents their appearance in a horizontal section of a portion cor- 
responding to that divided vertically in fig. 24 d. 26 a, a are the outer and more con- 
* The fibrous membrane lining the canal of the chorda dorsalis of the common Dog-fish {Spinax acanthias) 
exhibits a very similar structure. 
