Of the Substance of Bone, or Ilyalilie Substance.—The substance of bone has been considered, with but one-or two exceptions, as homo geneous, and without appreciable structure. If it be examined how ever under advantageous circumstances, with high magnifying powers, there will be no difficulty in detecting a very definite though delicate structure. A very small portion of a thin plate of bone should be taken for the purpose of examination : such may bo found in the cthmoid bone of small animals, as of the rat. If the piece is properly chosen it will be found to contain no Haversian Canals nor corpuscles, but will be extremely thin and transparent. A piece of this kind will present a delicate granular aspect with the surface nodulated. This granular appearance proceeds from the substance of the bone hieing composed of minute irregularly spherical granules. This structure may be traced with out much difficulty in any specimen of bone, although it varies much in distinctness in different specimens. The object should be placed between two slips of glass with a little plain water for examination. A delicate spiculum from the point where ossification is going on illustrates the granular tissue ex ceedingly well. The granules may be obtained separated from each other, so that each indi vidual may be examined independently of the others. When seen in this manner they exhibit a tolerably regular character, being mostly spherical, though a few have an oval form. hi a few specimens the oval form predominates.
Of the Lamincr.—Tho form assumed by the osseous tissue is that of lamina', and these laminae have a definite arrangement, so much so that three distinct systems are recognised, namely, laminte of the Haversian Canals ; secondly, the lamina: which connect the Haversian systems ; and, thirdly, the laminae which form the surface of the bone, and inclose the two previous orders- The laminre of the Haversian Canals have a concentric arrangement, and when divided transversely present a series of more or less distinct and perfect rings They vary very much in number, but the most common amount is ten or twelve. Of these, the internal lamina, that which forms the paricties of the llaversian Canal, is most distinctly marked, while each succeeding one as we proceed outwards becomes leas distinct. Connecting these Haversian systems is a second series of lamina', without which the former would exist but as a bundle of loose tubes (fig. 1, c). Li this substance we find the laminated arrangement less distinct, far less regular, and the laminae individually subject to great irregularity of thickness. They are generally more transparent than either the Haversian or external system. The last division consists of those lamina' which surround the exterior of the bone. These have greater individual extent, but are the least numerous. They are continuous with the lamina; of the Haversian system whenever the latter arrive at the surface of the hone; the external !aniline in this case being continuous with the inner laminre of the Haversian system.
The effect of madder upon the osseous system, when given to an animal with its food, may hero be noticed, since the colour is imparted to the lamina'. By introducing madder into the stomach, a deep red tinge is very soon observed : in a pigeon the bones were rendered brilliantly red in 24 hours. A similar effect was produced on a young
pig in three weeks. On making sections of bone so affected, the colour is found to be present. in the external 'imbue of the bone, and in the inner lamina) of the Haveraian system, thereby proving that the action of colouring takes place upon those surfaces which lie in contact with vessels.
Of the Haversian Canals.—These canals must be considered in rela tion to their number, their size, and the parts which they contain. The number of canals in a given space varies perhaps a ittle, but this variation will be regulated in some degree by the situation of the bone, but more especially by its age. Thus the transverse section of the femur of a human foetus of seven months will present many more canals than a section of equal measurement from the femur of an adult. The size of the Haversian Canals takes a considerable range, varying from the 300th to the 500th of an inch. The Haversian Canals undoubtedly give passage to blood-vessels, this being their principal if not only purpose.
The Corpuscles or Cells of Bone cannot be described as having any definite unvarying shape or size. The general form is a compressed oval, though not unfrequently they are circular. Again, they are sometimes almost triangular in their outline, while in other instances they approach a linear shape. These are the most common varieties of outline to which the bone-cells are subject, as they occur in the bones of man and the higher animals. In the four great classes of animals, namely, mammalia, birds, reptiles, and fishes, it has been shown by Professor Quekett that there are certain characters connected with these cells by which a bone of one class of animals may be distinguished from that of another, and that the size of these cells bears a direct relative proportion to that of the blood-corpuscles. He has shown that they are smallest in birds, a little larger in mammals, and largest of all in the reptiles ; while in fishes they are altogether unlike thbse in the proceeding classes. The importance of this obser vation in relation to fossil osteology is obvious. Connected with the cells are numerous delicate branching tubes, called canaliculi, which are slightly dilated as they enter the cells. The number arising from each cell does not allow of any very definite enumeration, since no two cells will be found possessed of a like number of branching tubes. The general arrangement of the tubes is radiate as regards the cells which form their common centre. The connections are so numerous between the tubes and between the cells through the tubes, that a fluid introduced into one cell in a bone, may enter every other cell in that bone. The cells are situated between the laminae, or on their surface ; but where concentric laminae occur, a9 in the Haversian system, the °ells are placed in circular lines between the lamina, each line of cells having the Haversian Canal as an exit common to it and the connecting laminae. When the canals for vessels are in great abundance, the bone-cells are more rarely met with ; indeed in some cases they are almost entirely absent. When the cells are seen by transmitted light, particularly in a transverse section of bone, they are frequently opaque. There is no doubt that the bone-cells perform the function of circulation.