74 Miscellaneous. MISCELLANEOUS. On the Development of the Purkinjean Corpuscle in Bone. Schwann, in his ' Mikroskopische Untersuchungen,' considers that the Purkinjean corpuscle of bone is derived from the pre-existing cartilage-cell, and that the canaliculi are prolongations, or protru-sions of the cell-wall. Many later authors, among whom are Gerber, and Todd and Bowman, express the opinion that it originates in the nucleus of the temporary cartilage-cell, and Tomes entertains the idea, that after the formation of the osseous tubes, in the process of ossification, the latter are filled up by a deposit of osseous granules, and while this deposit is going on, small cells are left, which are the rudimentary Purkinjean corpuscles. Henle thinks them to be the cavities of cells, the thickened walls of which are pierced by the canaliculi. Hassall confirms the view of Schwann, by stating, " the bone-cells (Purkinjean corpuscles) are to be regarded as complete corpuscles, the canaliculi of which are formed by the extension of the cell-wall, which is proved by watching the formation and de-velopment of bone.'' The opinion of Schwann and Hassall I can fully corroborate from my own observations upon an ossifying frontal bone, from a human embryo measuring 2 inches from heel to vertex. Each lateral half of the bone is about 31 lines in diameter, and presents to the naked eye the appearance of a delicate and close network, arising from the numerous areolae occupied by temporary cartilage. The frontal and orbital plates, it is worthy of incidental remark, at this period are nearly on a plane with each other, or are connected to-gether at a very obtuse angle along a central, transverse, crescentic, raised line, the rudimentary supra-orbitar ridge. The mode of development of the Purkinjean corpuscle, as noticed upon the upper or posterior border of the os frontis, is briefly as follows : — After the primitive ossific rete has been formed from the deposit of the osseous salts, enclosing groups of cartilage-cells in the areolae, the further deposit takes place in a fibrous or line-like course from the parietes of the areolae of the primitive osseous rete, in the interspaces of the cartilage-cells nearest to, or in contact with the sides of the areolae. At this period the cells shoot out or extend their canaliculi between the fibrillae just formed, and then the cell-wall and continuous walls of the canaliculi fuse with the translucent, homogeneous, or hyaline substance of the cartilage existing between the cells and the osseous fibrillae, and with the fibrillae themselves, by the deposit of the osseous salts. The period of the formation of the canaliculi appears to be quite definite, occurring during the de-posit of the osseous salts, and not before. To such an extent is this the case, that I noticed in several instances cells which had formed their canaliculi upon the side which was ossified, while upon the other side I could not distinguish any trace of them. During the whole time of the formation of the Purkinjean cor-puscle, the nucleus remains unchanged ; at least no change is per-ceptible in it beneath the microscope ; and by applying tincture of* iodine to the preparation, which turns the nucleus brown, I was able
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