220 MANUAL OF HISTOLOGY. 



cellular networks of many of the colourless connective-tissue corpuscles, 



with which indeed it most com- 

 pletely corresponds in the body 

 of the infant, where the body of 

 the cells have not yet become 

 filled with granules of melanin. 



This uncoloured state of the 

 choroid cells only persists in cer- 

 tain exceptional cases, until late 

 in life, through absence of pig- 

 ment. Thus among albinos, of 



. which we have always a ood 



the toe of a water-salamander. The observation example in white rabbits. As ;l 



SS d Ver " SPaC6< 5minutes - tAfter ^ rule,, it will be found that, soon 



afterbirth, the deposit of granules 



takes place in these cells, especially in their body and thicker part of 

 the processes. This pigmentation spreads likewise from the choroidea to 

 the cells of the lamina fusca, which is situated between the latter and 

 the sclerotic. 



A part also of the connective-tissue cells, of the iris, of dark but not 

 blue-eyed individuals, is likewise effected by it. But the colouring matter 

 appears here to be, as a rule, lighter, and of a clearer brown. 



If we examine the pigmentary connective-tissue cells of adult animals 

 or human beings (tig. 213), we are struck "by their irregularity of form, 

 which may be explained by the hindrance to their further development 

 through the deposit of melanin. For the same reason, the nucleus remains 

 here broad and oval, whereas in better-developed cells it usually becomes 

 long and narrow. 



Ifc is a point of special interest in viewing the stellate pigmentary cells 

 as modified connective-tissue corpuscles, that there exist gradations between 

 parts formed of them and purely fibrous structures. This is the case in 

 the lamina fusca, whose pigmentary cells are continuous towards the sclera 

 with ordinary colourless connective-tissue corpuscles. Pigmentary con- 

 nective-tissue cells are usually found also in the pia mater of the medulla 

 oblongata, and the adjacent portions of the cord, in adults. Their colour 

 is brown or blackish, and their quantity and distribution, moreover, liable 

 to variation. 



In diseased states of the tissues we may likewise find transitions of this 

 kind, and an abundant development of pigmentary cells. 



133. 



Many widely different parts are reckoned among the formed connective- 

 tissues. 1. We commence with the cornea. No connective-tissue structure 

 has so frequently been the subject of research as it. 



The cornea (fig. 215) presents for our consideration on its anterior 

 aspect, the laminated epithelium of the conjunctiva (d), while the posterior 

 surface is clothed with a layer of simple pavement cells (e), a so-called 

 endothelium. "Under each of these layers we come next upon a trans- 

 parent structureless membrane or lamella, of which that on the anterior 

 surface is. not easy of isolation, whilst that on the posterior aspect appears 

 stronger and easier to separate, as has long been known. 



The first of these, the lamina elastica anterior of Bowman (which is, 

 however, said to have an extremely dense fibrillated texture, by Rollc.tt 



