TISSUES OF THE BODY. 



191 



The vitreous humour is the most posterior of the refracting media of 

 the eye. Its refractive index is (taking water to be 1'3358) 1'3506 in 

 the human being (Krause). If destroyed it is not regenerated. 



REMARKS. Besides the German literature, comp. Bowman, Lectures on the Parts, 

 <fcc., of the Eye, London, 1849, p. 100. 



H6. 



Again we find gelatinous tissue presented to us in a higher state of 

 development (setting aside the tissues of the membranes of the ovuin), in 

 the first place in the enamel organ, then in the gelatin of Wharton, and 

 finally in the formless connective-substances of embryos. 



Here we find universally, in a transparent gelatinous substance, fusi- 



Fig. 181. Cells from the 

 enamel organ of a foetus 

 four months old. At a, small; 

 at 6, larger and more highly 

 developed stellate cells. 



Fig. 182. Tissue of the gelatin of Wharton in trans- 

 verse section ; from the cord of an embryo of four 

 months, o, a net-work of branching cells ; b, conden- 

 sation of the ground-substance forming bands ; c, un- 

 changed, roundish, formative cell. 



form and stellate cells, known since the days of Sclmann. These form 

 with their processes a cellular net- work, and lie at first somewhat closely 

 together, but after a while separate more widely one from another, a deposit 

 of the condensed intercellular substance forming around them. Thus we 

 have a system of reticulated bands within which the cellular net-work 

 still exists. ' The meshes enclose a soft and gelatinous mass in which 

 may be distinguished isolated unchanged formative cells. 



The substance, however, of which the enveloping bands are composed 

 commences early to present the appearance of being longitudinally 

 streaked. This gradually becomes more evident until the whole assumes a 

 fibrous condition, on which the mass is transformed into ordinary connec- 



