THE GENESIS AND STRUCTURE OF THE MEMBRANA TECTORIA 

 AND THE CRISTA SPIRALIS OF THE COCHLEA. 



BY O. VAN DER STRICHT. 



INTRODUCTION. 



The membrana tectoria belongs to a group of organs produced at the surface 

 of the epithelium and termed superficial cuticles or superficial cuticular formations. 

 Once developed, the generating epithelium persists in its entirety beneath the cuti- 

 cle or exceptionally may disappear, as in the case of the ameloblasts, which atrophy 

 after forming the enamel at their bases. 



One may subdivide these structures into three groups: In the first the process 

 of development can not be doubted or denied. It occurs just within the super- 

 ficial layer of the cytoplasm and the cuticle produced remains in close contact, 

 even continuity, with the generating cells. Examples are the striated borders of 

 the columnar epithelium of the intestine, of the crypts of Lieberkiihn, of the con- 

 voluted tubules of the kidney, of the syncytial layer of chorionic villi in the human 

 placenta, and of osteoclasts. 



The second is represented by the series of reticulares or fenestrated membranes 

 covering the surface of sensorial epithelia for example, the reticular membrane of 

 the crista and macula acustica and the organ of Corti, the membrana limitans 

 externa of the retina, the membrana limitans olfactoria. The openings of the 

 membrane are traversed by the apices of sensorial cells, the hairs of the acoustic 

 cells, the rods and cones of the retina, the ciliated vesicles of the olfactory cells. 

 These membranes in adult sensorial organs are in close contact with the surface 

 of the epithelium, but are completely separated from the generating substratum. 

 Hence their origin must be studied during the embryonic period of their 

 development. Many authors regard them as a real cuticle derived from the free 

 surfaces of the subjacent, that is to say, sustentacular cells. N. Van der Stricht 



(1908) has demonstrated that the reticular membrane of the acoustic epithelium 

 is formed by a system of terminal bars closing the intercellular spaces between the 

 embryonic epithelial cells. G. Leboucq (1909) proved that the membrana limitans 

 externa of the retina is not formed at all by the Miiller cells, but by the closing bars 

 separating the apices of the rods and cones and Mtiller cells. The present writer 



(1909) found the membrana limitans olfactoria to have a similar origin. The zona 

 pellucida surrounding the ovarian ovum in mammals and traversed by the pro- 

 longations of follicular cells which reach the surface of the egg must be considered 

 as a fenestrated membrane of the same nature. According to the investigations 

 of Dubreuil and Regaud (1908), it is derived from exoplasmic fibers produced within 

 the intercellular spaces of the follicular cells. My own preparations of ovaries of 



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