vee ee eee ee = 
REMARKS ON THE FIGURES OF PLATE XII. 3 
cleavage to its parts. The half can only be bisected in 
one direction, as by the line 2; and the fourth is not to 
be symmetrically cleft by either the line 1 or 2 applied to 
it. Hence it would appear that the law of form is so 
imseparable from the law of symmetry, and that both are 
so absolutely dependent upon the creation of homologues, 
that the combined operation of the three is typified and 
embodied in the figure, which is capable of. being bisected 
transversely and antero-posteriorly. In the whole form 
we find homologous halves * and. homologous fourths. 
In the half, we only find homologous fourths of the whole ; 
and in the fourth, we discover a quantity incapable of 
being itself cleft symmetrically, because of its being a 
fourth of the whole. The opposite figures will verify 
these remarks, with this one exception, viz., that the fourth 
of the square fig. A” is still homologous as to form with the 
whole quantity, and is, like it, still capable of symmetric 
cleavage both ways. ; 
~The fact, therefore, to which the foregoing remarks 
would tend is this, viz., that the osseous quantity which we 
name vertebra in the mammal spinal axis, presents to us 
the same condition of symmetric cleavage as we find 
attaching to the semicircle of fig. A’, or the triangle of 
fig. A”; that there is for either figure but one median line, 
2; and also, that, as the duplicature of the semicircle and 
triangle, figs. A’ A” forms the circle for the one and the 
| quadrilateral figure for the other, both of which have now 
become symmetrically cleavable by the lines 1 and 2, so 
does the duplicature of the vertebral quantity in figs. A’, 
A”, gain the like condition of symmetric cleavage by the 
lines 1 and 2; and hence, as the semicircle is half of the 
circle, so may the vertebra be a proportional of a whole 
quantity cast in dorso-ventral as well as lateral sym- 
metry. 
* In Geometry, the word “homologous” means corresponding; thus, the’ halves of equal things are equal, corresponding, or homologous ; 
consequently, the doubles of equal halves produce equal wholes, which are homologues. 
——- hh 
