' physi 
?s, the 
the sudden tension of the chordse tendinege resulting from the con- 
traction of the auricular muscle fibres which go down into the 
auriculo-ventricular valves. The author is hence forced to a belief 
in the existence of a nervous mechanism for the propagation. What 
this mechanism is, is not known, but it is possible that an extensive 
nerve plexus exists throughout the whole of the cardiac wall. Pas- 
sage of the contraction through the substance of the auricle is inde- 
pendent of the great nerve-trunks, since these may be destroyed and 
the wall even cut into zigzag strips without interfering with the 
Connections of Membranous Labyrinth, — In Fishes, Amphib- 
as, and Reptiles the duchis endolpnphaticns of the inner ear has 
long been known not to constitute a closed cavity, but to 
s, and Reptiles the duchis endoli/fvphaimis 
ig been known not to constitute a closed cavity, but to ]om tuc 
exterior (Elasmobranchs) or the lymph-spaces of the cranial cavity 
Riidingeri finds an analogous arrangement to exist in mammals and 
The ductus does not here end blindly, as has hitherto been 
but by means of several branched canals 
^t^rwiti 
The author regards the ductus as an elastic bag, the function of 
which is to enable the differences of pressure occurring within the 
labyrinth to be readily balanced. The size, the bladder like form, 
and the situation of the ductus in the cranial cavity, instead of 
within the bony labyrinth, favor such a theory. 
Function of the Cochlea.— The most commonly accppted 
hypothesis regarding the mode of analysis of composite sounds by 
the cochlea is that of Hensen, according to which a small portion of 
the basilar membrane is put into vibration by the incoming waves ; 
deep tones affect the membrane where it is widest— i.e., at the apex of 
the cochlea; high tones affect the narrow portion at the cochlear base. 
This theory is supported by an observation of Munk that a dog, in 
whom the base of the cochlea had been injured, could hear low tones 
only. Stepanow^ has recently tested the theory experimentally by de- 
stroying the apex of the cochlea in the guinea-pig, in which animal the 
cochlea projects freely into the auditory bulla. Different instru- 
ments, comprising the violin, piano, harmonica, Galton's whistle, 
B-bass, tuning-fork, etc., were employed to test the power of hear- 
ing; and the perception of sound was inferred from the reflex move- 
ment of the ears. In spite of destruction of a considerable portion 
of the apical region of the cochlea, accompanied by loss of en- 
dolymph, the animals reacted to all tones, and, what is especially 
' Sitzungsber. d. math.-phys., CI. d. k. baver., Akad. d. Wiss., 1887. 
Heft. 3, p. 4o5. Cf. Miinchener Med. Wochenschr., 1888, p. 139. 
' Monatschr. f. Ohrenh., xxii., p. 85. Cf. Centi-alblatt f, Physiologie, 
