cxiv BONE. 



and had been formed before any madder was given, had become much thinner; 

 showing that absorption takes place from within. In this last modification of the 

 experiment also, as noted by Mr. Hunter, a transverse red mark is observed near the 

 ends of the bone, beyond which they are white ; the red part indicating the growth 

 in length during the use of the madder, and the white beyond, that which has taken 

 place subsequently, thus showing that the increase in length is caused by the 

 addition of new matter to the extremities.* But other changes take place in the 

 bone. The spaces in the cancellated structure become enlarged, as well as the 

 medullary canal, by absorption ; whilst in other parts the tissue becomes more com- 

 pact by farther deposit on the inner surface of the vascular cavities. The sides of the 

 shaft in particular acquire greater solidity by the narrowing of the Haversian canals, 

 within which the vascular membrane continues to deposit fresh layers of bone ; and 

 madder administered while this process is going on, colours the interior and recently- 

 formed laminae, so that in a cross section the Haversian apertures appear surrounded 

 with a red ring. Lastly, Tomes and De Morgan have shown that in bones which 

 have acquired their full size, a production of new systems of Haversian lamellae con- 

 tinues throughout life, as described at page xciii. 



From the foregoing account it is evident that a great portion of a long bone is 

 formed independently of cartilage. Those physiologists, therefore, appear to have 

 reason on their side, who consider the pre-existence of that tissue as not being a 

 necessary condition of the ossific process, and who regard the precursory cartilage of 

 the foetal skeleton in the light of a temporary substitute for bone, and also as 

 affording as it were a mould of definite v figure and of soft but yet sufficiently con- 

 sistent material in which the osseous tissue may be at first deposited and assume a 

 suitable form. In fact the cartilage-cells are not ossified, and, as to the slender walls 

 of the primary areolae formed by calcification of the intercellular cartilaginous 

 matrix, most of them are, in a long bone, swept away by absorption, in the excavation 

 of the medullary canal ; so that they can only remain coated, however, and obscured 

 by secondary laminated deposit in the cancellar structure of bones which begin to 

 ossify in cartilage, t 



The time of commencement of ossification in the different bones, as well as the 

 number and mode of conjunction of their bony nuclei, are subjects that belong to 

 special anatomy. It may, however, be here remarked in general, that the commence- 

 ment of ossification does not in all cases follow the order in which the bones appear 

 in their soft or cartilaginous state. The vertebrae, for instance, appear as cartilages 

 before there is any trace of the clavicle, yet 'ossification begins in the latter sooner 

 than in any other bone of the skeleton. The time when it commences in the clavicle, 

 and consequently the date of the first ossification in the skeleton, is referred by some 

 to the seventh week of intra-uterine life ; others assign a considerably earlier period ; 

 but owing to the uncertainty that prevails as to the age of early embryos, the dates 

 of commencing ossification in the earliest bones cannot be given with precision. 



In regard to the number and arrangement of the nuclei, the following general facts 

 may be stated : 1. In the long bones there is one centre of ossification in the middle, 

 and the ends are for the most part ossified from separate nuclei ; whilst a layer of 

 cartilage remains interposed until the bone has nearly attained its full length. By 

 this means the bone is indurated in the parts where strength is most required, whilst 

 its longitudinal growth is facilitated. 2. The larger foramina and cavities of the 



* M. Flourens has repeated and varied these experiments, and represented the results 

 in beautiful delineations. Eecherches sur le Developpement des Os et des Dents. Paris, 

 1842. 



t Nesbitt, in 1736, maintained that the cartilage is "entirely destroyed;" he there- 

 fore considered it to be a mere temporary substitute ; but the steps of the process of 

 intracartilaginous ossification as now traced with the aid of the microscope were un- 

 known to him. The view stated in the text, together with most of the facts adduced in 

 support of it, was published in the fifth edition of this work in 1846, but, notwith- 

 standing the comprehensive researches of Bruch, by which he was led to the same opinion 

 (Denks. d. Schweitz. naturf. Gesells. 1852), it met with little notice, and probably less 

 assent, until the subject was treated of in a special memoir by the late H. Miiller (Zeits. 

 fur wissensch. Zool. vol. ix., 1858), Jx> whom the doctrine in its modern shape is now 

 commonly ascribed. 



