Of the larnine.—The form taken by the bone substance is that of laminm, and these laminm have a definite arrangement, so much so that three distinct systems may be recognised, namely, laminze of the Haversian canals ; secondly, the laminm which connect the Haversian systems ; and thirdly, the larninm which form the surface of the bone and enclose the two previous orders.
The laminm of the Haversian canals have a concentric arrangement, and present, when divided transversely, a series of more or less distinct and perfect rings : seefigs.448 and 950. They are subject to considerable variety in number, but the more common amount is ten or twelve. Of these, the internal lamina, that which forms the parietes of the Haversian canal,is most distinctly marked, while each succeeding one as you proceed outwards becomes less distinct. The concentric laminze with bone cells and central canal have received the name of Haversian system from Dr. Todd and Mr. Bowman in their work on Physiology.
Connecting these Ilaversian systems is a second series of laminm, without which the former would exist but as a bundle of loose tubes. (Seefig. 448, c).
In this substance we find the laminated arrangement less distinct, far less regular, and , the laminm individually subject to great f irregularity of thickness. It is often also more I transparent than either the Haversian or eater nal system. I3one cells contained in it are also more irregular in shape than those found in other situations. The last division consists of those laminm which surround the exterior of the • bone. These have greater individual extent, but are the least numerous. They are continuous with the laminm of the IIaversian system whenever the latter arrive at the surface of the bone ; the external laminx in this case being continuous with the inner laminm ot' the Haversian system.
Some authors have doubted the existence of a laminated arrangement in bone. lf, however, young bone be examined, all doubt upon the subject will be dispelled, and especially if it be first macerated in weak muriatic acid, when the appearance represented in fig. 450 will be seen. In bone so treated the laminze may with the assistance of two needles be separated. In
the, bones of old animals the laminm are much less distinct ; in these, however, they may be de monstrated if acid be used. Though the external larnina is very distinct, and therefore the boun dary of each Ilaversian system, yet in bone of advanced age the distinctness is lost in com mon with the definite outlines of the three orders of laminm. The cancelli of the can cellous portion of bones are but enlarged Haversian canals, which in addition to vessels contain fat ; the laminm therefore vthich form the walls are those of the Haversian system.
In connection with this division of the sub ject, the effect of madder. given to an animal with its food upon the osseous system may be noticed, since the colour is imparted to the laminm. By the taking of madder into the stomach the effect of giving a deep red tinge is very soon observable. In a pigeon the bones were rendered brilliantly red in twenty-four hours. In a young pig a similar effect was produced in three weeks.
On making sections of bone so affected the colour is found to be present in the external laminm of the bone, and in the inner Minium of the Haversian system, thereby proving that the action of colouring takes place upon those sur faces which lie in contact with vessels. This fact, with many others in this article, was men tioned in a paper by the author read before the Royal Society in June of 1838.
Of the Huversien eands.—These canals have to be considered in relation to their num ber, their size, and the parts which they contain. The number of canals in a given space is perhaps a little variable, but this variation will be regulated in some degree by the situation of the bone, but more especially by the age of the bone. Thus the transverse section of the femur of a human fcetus of seven months will present many more canals than a section of equal mea surement from the femur of an adult.
In certain fish of which the Scares is a spe cimen, the Haversian canals are extremely nu merous, so that bone cells become unnecessary, for here we find very few indeed, and in some sections none. ( Fig. 451.) give exit to their vessels upon the surface of the bone generally, while the large canals give entrance to arteries.