CONTAINED PERIOTIC TISSUE-SPACES IN THE HUMAN EMBRYO. 9 



them from the " endolymphatic " cavities of the membranous labyrinth. These 

 terms, together with the terms "perilymph" and "endolymph" for their contained 

 fluids, seemed particularly appropriate and in practical use have proved to be very 

 convenient. Since Breschet's time, however, the lymphatic vascular system has 

 taken on an increased and individual importance, due to researches in which Amer- 

 ican investigators have taken a particularly active part, and it now seems impor- 

 tant to restrict the term "lymphatic" to it and its associated structures. 



Inasmuch as the tissue-spaces surrounding the labyrinth have no known con- 

 nection with the true lymphatic system, either in their origin or in their ultimate 

 relations, it follows that the use of the term "lymphatic" in connection with them 

 is misleading. It therefore seems advisable to eliminate it, even at the expense of 

 losing such a convenient terminology. As a substitute for " perilymphatic " the 

 term "periotic" was finally decided upon and will be so used throughout this paper. 

 In the formation of this adjective the Greek word ous, from which it is derived, 

 is used in the restricted sense of representing the essential sense-organ, that is, the 

 otocyst itself and eventually the membranous labyrinth. Inasmuch as numerous 

 words derived from the same source are in common use, it is felt that this term will 

 be readily understood. 



We shall speak of a periotic connective tissue that everywhere surrounds the 

 membranous labyrinth. This periotic connective tissue includes in part the fine- 

 meshed periotic reticulum, and in part the large walled-off periotic spaces with their 

 contained periotic fluid, the most prominent of which are the scala vestibuli, scala 

 tympani, and the vestibular cistern. For the term "endolymphatic" fluid one 

 could substitute "otic" fluid; we would then have "liquor perioticus" and "liquor 

 oticus." In all other instances, except when elsewhere specified, the Basillensis 

 Nomina Anatomica terms have been adhered to. The term "semicircular duct" is 

 used to specify the epithelial or membranous canal as distinguished from the carti- 

 laginous semicircular canal. This usage was recommended by Breschet and was 

 adopted in the BNA. It was not taken advantage of, however, by Retzius (1884) in 

 his monograph on the vertebrate ear, who used the term "semicircular canal" for the 

 epithelial channel as well as for the cavity in which it lies. The influence of this 

 great monograph has delayed somewhat the adoption of the BNA recommendation, 

 and one finds subsequent writers still following Retzius in this respect, among whom 

 may be mentioned v. Ebner, R. Krause, Rothig, and myself in previous papers on 

 the development of the membranous labyrinth. In a similar manner the usage by 

 Retzius of the term "anterior" canal instead of "superior" canal, as recommended 

 by the BNA, has occurred in relatively recent papers, including, it must be con- 

 fessed, those of my own. In the present paper, however, this usage has been cor- 

 rected. In the historical review which follows the various structures mentioned 

 will be largely referred to in the older terms used by the respective authors. 



