86 CARNEGIE INSTITUTION OF WASHINGTON. 



First Evidences of the Eye and Ear. 



Professor G. W. Bartelmez, of the University of Chicago, in conjunction 

 with Dr. H. M. Evans, undertook in 1915 a study of young human embryos 

 during the period of somite formation. The work is now nearly finished and 

 is being prepared for publication. Certain features of the early history of the 

 nervous system have been made the subject of an independent study by Dr. 

 Bartelmez and his paper has recently appeared. In this he deals especially 

 with the origin of the otic and optic primordia, basing his observations on 12 

 normal human embryos, of stages ranging from 3 to 16 somites. His account 

 gives us for the first time an adequate picture of the earliest stages in the 

 development of these sense organs. He finds that the acoustico-facial gang- 

 lion is unquestionably derived from the wall of the definitive neural tube, 

 being delaminated from the dorsal part of the neural fold before the process 

 of tube formation is completed. As for the geniculate ganglion, he finds that 

 it is derived, in part at least, from the epibranchial placode of the hyoid arch. 

 His observations indicate that the gustatory ganglion cells of the ninth and 

 tenth cranial nerves, as well as those of the seventh, are derived from epi- 

 branchial placodes, whereas the other elements are probably derived from the 

 neural crest. Owing to the conflicting results obtained by investigators from 

 experiments in the production of cyclopia, the observations of Dr. Bartelmez 

 on the origin of the optic vesicles are of particular interest. He finds that 

 from the outset these vesicles are lateral in position and are not of median 

 origin. The development of the otic primordium before the optic in man 

 appears to be unique. It is explained partly by the fact that the otic plate is 

 formed at an extraordinarily early period, being recognizable at 2 to 3 somites, 

 and partly by the fact that the optic primordium is differentiated relatively 

 later than in most other mammals. 



Cerebrospinal Fluid. 



In previous reports mention was made of the studies of Professor L. H. 

 Weed upon the effect of intravenous injections of hypertonic and hypotonic 

 solutions upon the pressure of the cerebrospinal fluid. The fact that in this 

 way one can, to a considerable extent, control the brain volume has given an 

 immediate practical value to these observations and has led to their clinical 

 application in man. During the past two years Dr. Weed, in conjunction 

 with Dr. Walter Hughson, has extended this series of experiments to include 

 observations upon the arterial and venous pressures in relation to the cerebro- 

 spinal fluid. With a technical control that permitted the determination 

 of the effect of the manipulative procedure upon the pressure of the cerebro- 

 spinal fluid, they have been able to obtain some knowledge of the range and 

 variability of the normal pressure. From their studies it is shown that the 

 pressure of the cerebrospinal fluid practically always exceeds that of the 

 superior sagittal sinus (5 to 50 mm.). They also found that alteration in the 

 intracranial venous pressure effected alterations in the pressure of the cere- 

 brospinal fluid in the same direction but of lesser magnitude, and conversely, 

 alterations in the pressure of the cerebrospinal fluid caused changes in the 

 sagittal venous pressure of lesser extent but in the same direction. As for 

 the intracranial arterial pressure, this is evidently a factor of importance in 

 the maintenance of the pressure of the cerebrospinal fluid, though slight or 



