573 



BONE. 



BONELLIA. 



574 



action of colouring takes place upon those surfaces which lie in contact 

 with vessela 



Of the Haversian Cana.lt. 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 Haveraian 

 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 



Fig. 3. The Forms assumed by the Bone-Cells in Man. 





Fig. 4. Various Forms of Bone-Cells in the Bone of the Boa Cunitrictor. 



animala, 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 those 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 lamina;, or on their 

 surface ; but where concentric lamina; occur, as in the Haversian 

 system, the cells 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. 



Formation of Bone. The commencement of the growth of bone is 

 generally preceded by the formation of a cartilaginous matter which 

 occupies the place afterwards taken by bone. From this circumstance 

 it has been supposed that bone is formed from the ossification of cartilage. 

 This however is not the case, as it is found that although ossification 

 takes place in the first instance in cartilage, the bony matter thus 

 formed has not a permanent character. The formation of bone always 

 takes place in the first instance in the immediate neighbourhood of 

 blood-vessels in canals excavated in the cartilaginous substance, 

 and the spots where these canals are formed are called centres of ossi- 

 fication. There is usually one of these in the centre of a long bone 

 and one at each end, and frequently another for any considerable 



process or projection, such as the trochanter in the femur of the 

 human body. Up to the time that the bone is fully formed these 

 centres are only connected by cartilage, and this arrangement serves 

 the obvious purpose of allowing the increase of the whole bone by 

 means of cartilage until the time comes when no further increase of 

 size is needed. In the early conditions of the skeleton of the vertebrate 

 animals there is a much closer correspondence in this respect than is 

 subsequently seen ; for according to the habits of the animal the 

 whole of the cartilage is converted into bone, or by its absorption and 

 disappearance separate bones are formed. It is upon this fact that 

 the science of transcendental anatomy rests, in which the whole of the 

 modifications of the vertebrate skeleton are referred to departures 

 from a type which is found generally to exist in the embryo condition 

 of the whole class. Thus it is found, from an extensive comparison, 

 that the regular number of distinct bones in the wrist (carpus) and 

 instep (tarsus) is ten, but in the human wrist the number is reduced 

 to eight and in the instep to seven, whilst the reduction is still greater 

 in the hoofed mammalia. [SKELETON.] 



The structure of the temporary cartilage of bone is precisely the 

 same as permanent cartilage. The first calcareous deposit is made in 

 the space between the proper cells of the cartilage. These cells 

 subsequently disappear leaving large open areolse having no very 

 definite form. In these areolse there is subsequently deposited a 

 fluid blastema containing cells, and through the agency of this 

 blastema the Haversian canals and cancelli appear to be formed, 

 whilst the interspersed cells are changed into the bone-cells and their 

 projecting canaliculi. Although in most instances the formation of 

 bone is preceded by that of cartilage, yet this is not universally the 

 case, as we see bone formed in the substance of the tissues, as for 

 instance the fibrous membrane. This is seen in the development of 

 the bones of the roof of the skull, and also in the growth of bones 

 subsequently to their first development by the progressive calcifica- 

 tion of the inner layers of the periosteum, or fibrous covering of the 

 bones. 



It has been stated that the central cavities of some of the larger 

 bones are filled with the substance called marrow, an oily matter 

 contained in a series f membranous cells, which, like those in which 

 the fat is deposited do not communicate with each other. Even the 

 pores and cancelli of bone also contain a kind of oily matter, which 

 is supposed to differ from marrow only in possessing a greater degree 

 of fluidity. This oily matter is deposited in longitudinal canals, 

 which pass through the solid substance of the bone, together with its 

 nutrient vessels. The use of the marrow, and of the modification of 

 it which constitutes the oily matter, is not well understood. Without 

 doubt it serves the same general use in the economy as the other oily 

 secretions. [ADIPOSE TISSUE.] 



All bones are covered by a membrane, named, on account of its 

 affording them an external envelope, Periosteum. The outer surface of 

 this enveloping membrane is connected to the surrounding parts by 

 cellular tissue, but its inner surface is firmly adherent to the substance 

 of the bone. This adhesion is effected by innumerable fibres or 

 threads, which on examination are found to consist of blood-vessels. 

 The periosteum is in fact the membrane on which the nutrient 

 arteries of the bone rest, divide, and ramify in order to enter the 

 osseous substance. These threads are much more numerous in the 

 child than in the aduit ; and accordingly the adhesion of the perios- 

 teum to the bone is much firmer in the former than in the latter, as 

 the quantity of blood distributed to the bone is greater. Moreover, 

 in general the inner surface of bones is also lined by a fine and 

 delicate membrane, commonly termed the internal periosteum, the 

 continuation of which forms the membranous bags in which the 

 marrow is contained. 



(Roget, Animal and Vegetable Physiology ; Southwood Smith, 

 Philosophy of Health ; Simon, AniiniU (.'In inisinj ; Sharpey, (fiwins 

 Anatomy; Cyclopedia, of Anatomy and Physiology, articles ' Bone,' 

 ' Osseous Tissue' ; Todd and Bowman, Physiological Anatomy; 

 Carpenter, Principles of Physiology, General and Comparative; 

 Tomes and De Morgan, Structure of Bone, Phil. Trans. ; Quekett, 

 Lectures on Histology.) 



BONE-BEDS. Accumulations of the bones of extinct animals, more 

 especially of fish and Saurian reptiles, are not uncommon in various 

 strata, and have had this name given them by geologists. They gene- 

 rally occur at the termination of one formation and the commencement 

 of another. These Bone-Beds are local, and are not in any case very 

 extensive. The thickest and most widely-distributed is that of the 

 Lias, which seems to mark the commencement of the New Red-Sand- 

 stone epoch. The most remarkable Bone-Beds are the following : 



Bone-Bed at the base of the Lower Greeusand at its junction with 

 the Wealden ; at the base of the Inferior Oolite, at its junction with 

 the Lias ; at the base of the Lias, at its junction with the New Red- 

 Marl ; at the base of the Mountain Limestone, at its junction with the 

 Old Red-Sandstone ; at the base of the Old Red-Sandstone, at its junc- 

 tion with the Ludlow Rock of the Silurian System. 



(Brodie, On the Basement-Beds of the Inferior Oolite ; Prof. Geol. Soc. 



BONE-DOG, a name given in Sussex to the picked Dog-Fish (A can. 

 thins r,il,/,ir!f, Hisho). [SQUALID*.] 



BONE'LLIA, a genus of Echinodermata, formed by Rolando, and 

 placed by C'uvier in the tenth order of his first class of Zoophytes, the 



