ORGANS OF THE BODY. 



633 



to these stronger bands, and passing into them without any sharp line of 



distinction, we find at certain points, but especially in the molecular 



(g) and intergranular layer 



(d), an extremely delicate 



porous or spongy tissue (e), 



like that already met with 



in the grey matter of the 



nervous centres. This (neu- 



roglia) has been regarded by 



some as an artificial product, 



formed by the coagulating 



action of the chromic acid 



on some of the fluids of the 



tissue (Henle). 



The spongy substance in 

 question is so delicate in man 

 and many other mammals, 

 that with weak microscopic 

 power we are only able to 

 make out a dotted mass, 

 perhaps adherent to the fibres 

 of Mutter. Very strong 

 lenses, on the other hand, 

 reveal its reticulated struc- 

 ture and connection with the 

 sustentacular bands, whose 

 outline on that account is 

 by no means smooth. In 

 different portions of the 

 retina, however, this susten- 

 tacular matter presents much 

 variety. In some of the 

 nodal points nuclei are to be 

 seen, so that here again we 

 have the cellular equivalents 

 of the grey matter of brain 

 and spinal cord. In the in- 

 ternal granular layer the 

 fibres of Muller are observed 

 to be possessed invariably of 

 elongated nuclei (e r ). 



The sustentacular matter we are considering extends as far as the 

 internal surface of the so-called rod-layer (columnar). 



Here we find a repetition of the relations already seen at the internal 

 surface of the retina, although less marked, namely, a fusing together of 

 the fibres of Muller to form a cribriform limiting membrane. To this 

 (a, a), which u'sually presents itself in vertical section as a sharply 

 defined line, the name of membrana limitans externa has been given 

 (Schultze). But the name is unfortunately selected, for many of these 

 bands of Muller apparently terminate before reaching it, in the first place 

 namely, in the intergranular layer, or even deeper still \ and then, again, 

 as very recent observations show, the connective-tissue sustentacular 

 matter does not cease at the membrana limitans externa. It extends 



Fig. 588. Diagram of the retina, after Schultze, with its 

 connective-tissue portion, a, Membrana limitans externa ; 

 e, radiating, or Miil/ers sustentacular fibres, with their 

 nuclei ef ; d, framework of the intergranular, and gr, of the 

 molecular layer ; I, membrana limilans interna. 



