DEVELOPMENT OF BONE. 277 



deposits ; and into the origin of these, we have now to inquire. According to 

 the views of Messrs. Todd and Bowman, and of Mr. Tomes (Op. cit.), the cells 

 of the blastema fill themselves with ossific matter, except at the points occupied 

 by the nuclei; at the same time, they become flattened against the walls of the 

 canals, and their nuclei send out radiating prolongations ; so that, when the 

 calcification of the cell has been completed, a stellate cavity is left in the hard 

 deposit, which is occupied by the granular matter of the nucleus. The centre 

 of this cavity forms the lacuna, in which some traces of the original granular 

 matter may frequently be found remaining; whilst its prolongations form the 

 canalicuU, from which the nuclear matter seems afterwards to disappear altogether. 

 By Henle', again, it is considered that the lacuna is a cavity left in the centre 

 of a cell, which has been partially filled up by the deposition of calcifying matter 

 upon the internal surface of its wall ; and that the unequal deposit of this matter 

 leaves passages, resembling those of the " pore-cells" of plants, which constitute 

 the canaliculi. It is justly remarked, however, by Dr. Sharpey, that neither of 

 these two views is reconcilable with the structure of ordinary sound bone : in 

 which there is not only an absence of any vestiges of cell-boundaries, limiting 

 the radiation of the canaliculi which issue from each lacuna ; but it is constantly 

 to be observed, that the canaliculi of one lacuna encroach upon the areae traversed 

 by those of the next. And it is considered by Dr. S., that the lacunae and 

 canaliculi are " little vacuities left in the tissue during the deposition of the 

 reticular fibres, as open figures are left out in the weaving of some artificial fabrics ; 

 and thus that the apposition of the minute apertures existing between the reti- 

 culations of the lamellae gives rise to the canaliculi. At the same time it seems 

 not unlikely that a cell or a cell-nucleus may originally lie in the lacuna or central 

 cavity, and perhaps determine the place of its formation." (Op. cit., p. 91, vol. i., 

 Am. ed.) The Author has been led, however, from his own observations, to con- 

 sider with Schwann, that each lacuna, with its system of radiating canaliculi, is 

 one entire cell, resembling the pigment-cells of Batrachia (Fig. 87, c 7 c), which 

 send out stellate prolongations that sometimes inosculate with each other; and 

 to believe that these prolongations in their outward growth insinuate themselves 

 through the areolse of the fibrous basis, whilst it is undergoing calcification, after 

 the manner in which the rootlets of plants extend themselves through the loosest 

 parts of a dense soil. For he has traced all stages of gradation between the simple 

 rounded cavities, whose correspondence in size and situation with the cells that 

 are scattered in the midst of the consolidating blastema leaves scarcely any doubt 

 of their identity with these, and the lenticular lacunae with numbers of canaliculi 

 proceeding from them. 1 Whatever may be the precise mode of the production 

 of the lacunae and canaliculi, it may be considered as a well-established fact, that 

 the production of the concentric layers of osseous substance within the Haversian 

 canals takes place in a manner that more closely corresponds with the intra-mem- 

 branous, than with the intra-cartilaginous form of osteogenesis; and that thus 



1 The independent observations of Dr. Leidy of Philadelphia precisely confirm those of 

 the Author upon this point. (See the "Proceedings of the Philadelphia Academy of Natu- 

 ral Sciences," Nov. 1848). [Dr. Leidy was led to adopt the views of Schwann, in relation 

 to the development of the lacunae or Purkinjean corpuscles, from some observation made 

 by him upon the process of ossification in the os frontis of a human embryo, measuring 

 two inches from heel to vertex. According to this observer, each half of the os frontis 

 at this period presents a network of osseous tissue, which is thickest and most developed 

 along the curve of the supra-orbitar ridge, and the frontal and orbitar portions are nearly 

 on a plane with each other. When examined by means of the microscope, the interspaces, 

 or meshes of the osseous tissue are discovered to be filled with cartilage cells contained 

 in a transparent matrix or hyaline substance (Fig. 70*, b). The cells are isolated from 

 each other, granular in structure, and contain a large granular nucleus, within which 

 may be detected a translucent nucleolus. The cells contents are colored brown by iodine, 



