308 SPECIAL HISTOLOGY. 



lying in a clear fluid within them, and at the same time the cells slowly 

 increase in size. When the branchiae have disappeared, all the cartilage- 

 cells are already quite transparent, with distinct nuclei and walls, and 

 they now gradually increase to the size of 0-018-0-024 of a line, and 

 the nuclei to that of 0-005 and 0-007 of a line; the cells, from their 

 mutual pressure, become polygonal, and constitute one of the most 

 delicate cellular tissues possible. They now also begin to multiply by 

 endogenous cell-formation around portions of the contents (Nageli), so 

 that in each cell two secondary cells are formed around the two nuclei 

 produced from the original nucleus, and entirely fill it; at the same time 

 they again increase, though very slowly, particularly in certain carti- 

 lages of the head, until they attain a she of 0-013-0-018 of a line, and 

 in some places of not more than 0-006-0-013 of a line; whilst between, 

 them, a thick interstitial substance is formed out of the coalesced walls 

 of the different generations of cells. With respect to man and the 

 mammalia, it can only be stated as a supposition, that the cartilage-cells 

 originate in a modification of the primordial formative cells. This sup- 

 position is favored by the circumstance, that in a human embryo of 

 eight or nine weeks, the outer extremities of which were just developed, 

 they presented scarcely a trace of formed cartilage, the innermost cells 

 of the rudimentary extremities being hardly distinguishable from the 

 outer. They were 0-004-0-006 of a line, in size, spherical, with grayish 

 granular contents, and indistinct nuclei of 0-003 of a line, and formed a 



tissue of some consistence, without any appre- 

 ciable interstitial substance. The correspond- 

 ing cells in the embryo of a sheep 6-7 lines 

 in length were somewhat larger, although the 

 embryo was smaller than the human foetus 

 above noticed. In this case (Fig. 129) they 

 measured for the most part, 0-006-0-01 of a 

 line, had distinct walls, nuclei, and clear, 

 aqueous, only slightly granular contents, and 



were lodged in a scanty homogeneous interstitial substance, so that they 

 were only partially or not at all in contact with each other. The contents 

 of only a very few cells were still in the opaque condition, and these 

 were without any visible nucleus, others exhibited the commencement of 

 transparency from the metamorphosis of their contents. The further 

 development of the cartilage up to the end of foetal life, except in its 

 ossification, presents these characteristics, viz.: (1.) That the cells pre- 

 cisely like those in the batrachian larva, continually increase by endo- 

 genous cell-formation, whilst precisely as in the same instance, there is no 



FIG. 129. Cartilage-cells from the humenu of an embryo of the Sheep, 6 lines long: 

 a, cells with nucleus and clear contents (two cells retain remains of the earlier thick con- 

 tents) ; 6, cells with consistent contents, without visible nucleus; c, intercellular substance. 



