DEVELOPMENT OF THE SCALES AND BONES OF FISHES. 
689 
In the central convergent portions of each of these cartilaginous segments, there is 
a limited formation of chondriform bone (41 Jt) arranged around the canal of the 
chorda, and which must contribute materially to the strength of the bone by cement- 
ing together the thin internal borders of the wedge-shaped osseous segments. In- 
ternally, this chondriform bone is consolidated, presenting only tbe usual small cel- 
lular areolae; but external to this more solid structure is a fringe, consisting of innu- 
merable minute spherical granules of various sizes, and which obviously represent the 
early conditions of the same tissue. As in the case of the lenticular granules seen in 
the fibrous membranes of cycloid scales, these granules increase in size, partly by the 
addition of concentric calcareous layers applied to their exteriors, and partly by the 
amalgamation of detached granules, which are bound together by the addition of 
common concentric coverings. Thus the chondriform bone is constantly encroach- 
ing upon the inner extremities of the four cartilages, the cells of which are remark- 
ably elongated and fusiform, and radiate outwards in irregular lines, their long axes 
being disposed in the same direction. No chondriform bone invests the sides of the 
four osseous segments. Near the periphery of each cartilaginous segment the cells are 
more spherical, but still detached from each other and not arranged in the ordinary 
ichthyal groups seen at a greater distance from ossifying surfaces. On examining 
the outer margin of each cartilage, at its junction with the apophysis with which it 
is surmounted, we perceive that here also the former is being encroached upon by the 
latter. Each apophysis (41 h and i) consists of large cancelli, formed by lamincC of 
membraniform bone, and appears to be produced in the way already described, when 
speaking of some of the cranial bones. An irregular cavity is formed by the shrinking 
or partial absorption of the cartilage, which is afterwards lined by a fibrous membrane. 
This membrane becomes subsequently calcified, a copious development of chondri- 
form bone taking place at the same time within the contiguous cartilage ; hence a 
considerable amount of the latter structure (41 1) fringes the growing bases of these 
apophyses. There is great beauty in the way in which the various elements of the 
structure thus preserve their needful adaptation to each other. The enlargement of 
the divergent osseous segments by peripheral additions of membraniform bone, 
produces a corresponding increase in the intervening areas ; the more external cells 
of the cartilages by which the latter are occupied multiply consentaneously in the 
ordinary way. Though the apophyses are not in this instance anchylosed to the 
osseous centrum, but detached, it is still necessary, in order to obtain a degree of 
firmness, that the bases of the former should be immediately in contact with the 
radiating plates of the latter, and not merely perched upon the top of the terminal 
prolongation of the cartilage which always projects into their interior. As the super- 
ficial area of each cartilage is enlarged, a corresponding expansion of the growing 
base of each apophysis is produced, and the requisite adaptation of the one to the 
other is thus maintained. 
The four portions of chondriform bone (41 h) grouped around the canal of the 
