384 NORMAL HISTOLOGY. 



this peripheral lamella trabeculae extend across the intervening 

 perilymphatic space to the fibrous wall of the membranous laby- 

 rinth. The endothelium of the inner surface of the periosteum 

 invests the fibrous trabeculae as well as the outer or perilymphatic 

 surface of the membranous labyrinth. 



The walls of the saccule and the utricle consist of the con- 

 nective-tissue lamella, composed of the bundles of fibrous tissue 

 and the delicate epithelium. At the positions where the filaments 

 of the auditory nerve enter the maculae cribrosae and acusticae 

 the fibrous stratum is best developed and densest, forming a layer 

 .15 to .20 mm. thick. Within other parts of the vestibule, especially 

 in the roof of the utricle, the thickness of this layer may be reduced 

 to 5-6 {>.. 



The lining of the saccule and the utricle consists everywhere, 

 except at the maculae acusticae, of a single layer of thin flattened 

 polyhedral cells. Over the regions receiving the terminations of 



FIG. 396. 



d 



Section through membranous labyrinth of cat, showing specialized areas within 

 ampulla (A) and utricle (B) : a, surrounding bony wall separated from membranous 

 tube (6) by layer of areolar trabeculae (d) ; c, crista acustica covered with specialized 

 epithelium (/); e, e 1 , bundles of nerve-fibres ; g, ordinary epithelium ; k, layer of 

 otoliths overlying neuro-epithelium of macula acustica (/) ; i, blood-vessel ; k, fibrous 

 layer ; /, adipose tissue. 



the nerve-fibres, the maculae acusticae, on the contrary, the epi- 

 thelium undergoes marked alteration, changing from the indifferent 

 covering cells into the highly-specialized neuro-epithelium. At 

 the margin of these areas the cells are at first cuboidal, then low 



