300 GEOEGE L. STREETER 



dency is to restrict the use of the word 'lymphatic' to the lym- 

 phatic vascular system and its associated structures, with which 

 these ])ai"ticular spaces have no known connection, either in 

 their origin or in their ultimate relations. ^ We shall therefore 

 speak of a periotic connective tissue that everywhere surrounds 

 the epithelial portion of the labyrinth. This connective tissue 

 includes, in part the fine-meshed periotic reticulum, and in 

 part the large walled-off perioticular spaces to which belong the 

 vestibular cistern^ the scala vestibuli and the scala tympani 

 with whose development we are primarily concerned. 



MATERIAL AND METHODS 



The observations that are recorded in this paper are all based 

 on human embryos and cover the period included between 

 embryos 35 mm. and 130 mm. CR length, which is approxi- 

 mately equivalent to the period between the ninth and sixteenth 

 week of fetal life. 



To facilitate the determination of the form and relations of 

 the spaces, wax-plate models of the membranous labyrinth 

 and the surrounding spaces were reconstructed after the Born 

 method. Advantage was taken of the improvements in the 

 method recently devised by Lewis 1915.2 The serial sections 

 were photographed at a suitable enlargement on bromide paper. 

 By means of a preliminary model of the membranous labyrinth, 

 the necessary reconstruction lines were estabhshed and inscribed 

 on the bromide prints. From these prints then the membran- 

 ous labyrinth and the perioticular spaces were traced on wax- 

 plates. After cutting out from the plates the areas correspond- 

 ing to these structures, the plates were piled and the resultant 

 cavities were filled with plaster of Paris. The wax was finally 

 melted off and there was left then a permanent plaster cast of 

 the objects desired at a definite enlargement. Views of these 

 models are shown in figures 4 to 9. 



In outlining the periotic spaces it was found necessary to 



^ Sabin, F. R. Harvey Society Address. Science, vol. 44, 1916, p. 145. 

 2 Lewis, W. H. The use of guide planes and plaster of Paris for reconstructions 

 from serial sections. Anat. Rec, vol. 9, 1915. 



