CONTAINED PERIOTIC TISSUE-SPACES IN THE HUMAN EMBRYO. 11 



tions are principally based. He showed that the perilymph occupies all the space 

 of the bony labyrinth that is not taken up by the semicircular tubes, the utricle 

 (median sinus), and the saccule. It surrounds these everywhere and separates 

 them from the bony walls of the labyrinth. The perilymph also, according to him, 

 fills the spaces of the cochlea and circulates freely throughout the whole system. 

 The scala tympani is connected at its apical extremity with the scala vestibuli by 

 means of the opening to which he gave the name helicotrema. The scala vestibuli 

 in turn opens freely into the vestibule, into which also the semicircular tubes open. 

 He points out the fact, and discusses its relation to the mechanism of hearing, that 

 any vibrations transmitted to the perilymph by the foot-plate of the stapes would 

 be transmitted freely and evenly to the whole of the membranous labyrinth and to 

 the lamina spiralis. He describes the perilymph as consisting of a thin, watery, 

 saline fluid containing a small amount of albumin. He believed that it was secreted 

 by the thin, delicate membrane lining the cavity of the labyrinth and that the 

 materials were brought there by the small blood-vessels that supply this layer. The 

 aqueducts, according to him, are not for the transmission of perilymph, but only 

 serve as passages for veins. He regards them of embryological significance; that 

 they represent the remaining strands of connection with the dura mater, of which 

 the inner ear is a part that has been separated off by the enveloping growth of bone. 

 A description is given of the distribution of perilymph in different animals and it is 

 pointed out that in some fish it communicates with the fluid surrounding the central 

 nervous system and how in such cases the oily or gelatinous cerebro-spinal fluid 

 actually serves as the perilymph. Entirely distinct from the perilymph is the 

 endolymph, which is the fluid filling all parts of the membranous labyrinth. 



Breschet describes the character of the endolymph in different animals. He 

 shows that it always contains calcareous deposits, which he designates as otoliths 

 and otoconia, depending on whether they are in the form of lumps or dust. He 

 shows that these are distributed at definite places, at the points of nerve-terminations, 

 and suggests that they act as dampers that tend to check the prolonged vibration of 

 the endolymph. In comparing the ear with the eye, he suggests that the perilymph 

 bears the same relation to the organ of hearing that the aqueous humor bears to the 

 organ of vision. The vitreous body he considers analogous to the endolymph. 



Special emphasis has been given to the treatise of Breschet because it marks the 

 beginning of the modern epoch in the anatomy of the ear. Previously the descrip- 

 tions of this organ had been purely fragmentary. Breschet's monograph is both 

 comprehensive and analytic. If his treatise is searched for defects that are revealed 

 in the light of our present knowledge of the anatomy of the ear, one would name 

 perhaps only two major ones. One of these concerns the inaccurate and meager 

 nature of the embryological features as given by him, and the other concerns the 

 membranous cochlea, the existence of which was entirely unknown at that time. 

 It is interesting to note that these two defects prove to be related; that it was 

 through embryological investigations that the membranous cochlea was eventually 

 discovered. 



At about the time of Breschet's treatise, Huschke (1831) made the discovery 

 that the membranous labyrinth was originally a pit in the skin, a fundamental point 



