162 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
transverse process of the fifth vertebra, although neither flexible nor elastic, strongly 
resembles the two preceding processes. 
In reference to the movements of the tripus it seems to us not improbable that the 
relation of its crescentic process to the slit-like groove between the oval plate and the 
elastic root of the transverse process of the fourth vertebra must also, to some extent, 
limit and control the lateral motion of that ossicle, even if it does not altoerether 
prevent the possibility of any such movement, when the protractor muscle is quiescent 
and the plates are not pulled outwards and upwards. On the other hand, the 
contraction of these muscles, and the consequent upward and forward movement 
of the plates, will necessarily confer upon the tripodes a wider range of possible 
lateral motion. In fact, as we shall subsequently have occasion to point out more in 
detail, any increase in the volume of the anterior chamber of the air-bladder will 
mainly depend on the movements of the oval plates in the way just described, but 
it is precisely such movements that will give to the tripodes an increased range 
of lateral motion, and, at the same time, the capacity for registering the degree of 
distension of the bladder. Conversely, the compression of the air-bladder by the 
elastic recoil of the plates when their protractor muscles cease to contract, will 
necessarily have the effect of confining the movements of the ossicles within 
comparatively narrow limits. 
In the general structure of the various parts of the internal ear, and of the 
recesses in which they lie, Auchenipterus closely agrees with Macrones. 
Lateral cutaneous areas are well marked, but the oval plates of the “ elastic- 
spring ” mechanism, to a large extent, prevent the lateral walls of the anterior 
chamber from coming into direct contact with them, but behind the plates the lateral 
walls, and to some extent the outer walls of the lateral compartments also, are 
in close relation with these areas. The spaces between the plates and the superficial 
skin are occupied partly by the large protractor muscles, and partly by a yellowish 
fatty tissue. 
A uchenipterus ohscurvs. 
But for one or two minor points of difference, this species very closely resembles 
the preceding one. The superficial ossifications are somewhat more extensively 
developed, inasmuch as they extend on to and invest the lateral surfaces of the 
eighth vertebral centrum, so that the ninth is the first of the flexibly articulated 
series. A further distinctive feature is to be found in the presence of a small cmcal 
diverticulum which is given off from the posterior and outer extremity of each of 
the lateral compartments of the air-bladder, 
Euanemus. 
Since Johannes Muller (28) first recorded tbe existence of an “elastic-spring” 
