STRUCTURE AND DEVELOPMENT OF BONE. 
123 
a more opake and granular part, to which the former appears to be the matrix. Tlie 
peripheral lamina of the Haversian systems is generally clear and free from granularity, 
and the internal lamina sometimes presents a similar structureless appearance. The 
matter which fills up the Haversian systems in the full-grown antlers of the Cervidse, 
affords another and a very striking example of transparent structureless osseous tissue, 
which in this instance is the more distinct from the absence of canaliculi in its sub- 
stance. Then, again, we have another instance in the clear tissue which is some- 
times found between the superficial Haversian systems of ordinary bone. It has 
already been described as a non-laminated element found on the surface of certain 
bones. In the instances already cited, and no doubt in many others which may be 
found in the skeletons of the lower vertebrata, we have bone tissue without obvious 
granularity and without obvious structure, and although it forms but a small part of 
the general mass, yet from its constant presence at all ages and in all subjects, it 
must be regarded as an integral and normal part of mammalian bone. The granular 
condition of bone tissue is tolerably obvious in all preparations, though it is much 
more strongly marked in some specimens than in others. The amount of the com- 
ponent granules varies in different parts of the same specimen, and in specimens taken 
from different parts of the skeleton. Thus in one situation we may see laminae with a 
highly granular part gradually merging into a transparent tissue, while in another the 
laminae may be granular throughout. Again in young bone developed in cartilage, 
the part between the cells becomes highly granular ; fragments of which may be 
found in certain adult bones, as in the petrous portion of the temporal bone (Plate VII. 
fig. 16 h). Bone near the articular surface frequently presents a well-marked gra- 
nularity. Whether the granular and the transparent parts of bone contain different 
relative amounts of phosphate of lime is a question yet to be decided. 
Development of Bone . — Temporary cartilage, when it first appears in the embryo, 
consists of an aggregation of closely packed nucleated cells, which in the process 
of growth become separated by the development of a tissue external to them, 
usually designated the hyaline tissue of cartilage. At this stage of growth we 
have a granular cell occupying a cavity in the hyaline tissue ; at a previous period 
the granular cell was inclosed by an outer cell-wall, to which it formed the nucleus, 
but now the cell-wall has merged into the hyaline tissue, from which it can no 
longer be distinguished, while the granular cell contains itself one or more nuclei. 
In making sections of cartilage many of these granular cells escape from their 
cavities in the hyaline tissue, and may be seen detached and floating about in the 
field of the microscope. Some little confusion of terms has arisen in connexion 
with this part of the subject. The granular cells are not unfrequently described 
under the name of cartilage-nuclei containing nucleoli, while in fact they are cells 
capable of separation from the matrix, and are at one period the only recognisable 
cartilage cells. They occur singly or in groups, more frequently however two or 
three are extended in a line. It is proposed in the present communication to call 
