322 SPECIAL HISTOLOGY. 



nothing but a small quantity of fluid and many rounded cells, with one 

 or two nuclei and faintly-granular contents, of which I am unable to 

 say how they originate, but only this much, that they are altogether new 

 formations. In process of time these cells, which are in all respects 

 identical with those which occur, in the adult, in certain bones (vid. 

 supra), are developed in the usual way into connective tissue, blood- 

 vessels, fat-cells, and nerves. The formation of bloodvessels proceeds 

 with great rapidity, so that bones, very shortly after the development of 

 the medullary spaces, exhibit bloodvessels in them ; that of the fat and 

 nerves takes place more slowly, although the latter, at the period of 

 birth, of course with fewer filaments than subsequently, may be very 

 readily perceived in the large cylindrical bones, even more readily than 

 in the adult, because at this time the medulla may be more easily washed 

 away from them and the great vessels. The fat-cells at this period are 

 but few in number ; the medulla, in man at least, being colored entirely 

 red by the blood and the light reddish medulla-cells. After birth they 

 gradually multiply, till at last, the marrow, in consequence of their great 

 increase, and the disappearance of the medulla-cells, which are ulti- 

 mately all transformed into the elementary tissues of the permanent 

 medulla, acquires its subsequent color and consistence. 



In many of the primarily cartilaginous bones of Birds and Amphibia, 

 the ossification of the cartilage commences, according to Rathke and 

 Reichert (1. c.), on the outer aspect of the cartilage, so that at first a 

 cylinder of bone is formed with cartilage internally and at the extremi- 

 ties. The remainder of the internal cartilage then affords space to the 

 medulla, whilst the epiphyses are formed out of that of the extremities. 



If the contents of the cartilage-cells, the "cartilage-corpuscles" of 

 authors, be really surrounded by a membrane, as Yirchow supposes, it 

 may be assumed that a similar tunic, analogous to the primordial utricle 

 of the plant-cell (vid. sup. 8), exists also around the contents of the 

 bone-cells, and that it takes an essential part, by its throwing out stel- 

 late processes, in the first formation of the canaliculi, their further elon- 

 gation and ultimate anastomoses. In this case, also, the stellate and 

 readily isolated cartilage-cells from an enchondroma described by Vir- 

 chow (Wurz. " Verh.," Bd. 1), around the internal portions of which the 

 contours of rounded cells were visible, would be intelligible, and even the 

 possibility of the isolation of stellate organisms from normal bone (vid. 

 sup.) be explicable. My exposition of the formation of the lacunae in 

 rachitic bone, is confirmed by Rokitansky and Virchow (Wurz. " Verh.," 

 II.) ; whilst Robin declares that it is incorrect, giving a description of 

 their formation which is, to me, unintelligible. I recommend to his 

 notice rachitic bone, the cementum of the horse's tooth, and the symphy- 

 ses ( 95), with which he is manifestly unacquainted, and hope that he 



