236 Transactions.— Zoology. 
face closely applied against the posterior surface of the skull. Each cornu 
fits closely against the three facets already mentioned, and is strongly 
attached by fibrous tissue to y and z, as well as to the outer border of x. 
Over against the auditory fontanelle the wall of the bladder becomes 
considerably thickened, forming a pad (p) which fits tightly into the fora- 
men and comes in close contact with the lamina of the fontanelle, its surface 
presenting folds corresponding to those in the lamina. 
The outer or free end of each cornu of the air-bladder comes in close 
contact with the thin skin (fig. 8, a) immediately in front of the dorsal end 
of the shoulder-girdle and beneath the operculum (op). 
The arrangements described must form a fairly efficient transmitting 
apparatus to the organ of hearing. Sonorous vibrations meeting the thin 
subopereular skin, will be transmitted to the air in the air-bladder and 
thence to the auditory fontanelle, the vibration of which will act imme- 
diately on the perilymph. The subopereular skin will thus act as an im- 
` perfect tympanic membrane, the air-bladder as a tympanic cavity, and the 
auditory fontanelle as a fenestra ovalis. 
EXPLANATION OF PLATE XXXIII. 
Fig.1. Hinder view of the skull of Lotella bacchus (nat. size). 
1l 
au. f, right auditory fontanelle. 0p. 0, opisthotic. 
b. o, basi-oceipital. pt. o, pterotic. 
€. 0, ex-occipital. s. 0, Supra-ocipital. 
ep. 0, epiotic. z,y,z, facets for attachment of air- 
f.m, foramen magnum. bladder. 
l, lamina filling up left auditory fon- IX, X, foramen for exit of ninth and 
tanelle. tenth nerves. 
Fig.2. Anterior end of air-bladder opened from the dorsalside; p, pad fitting against 
: auditory fontanelle; 7, rete mirabile. 
Fig. 3. Transverse section taken just behind the head (diagrammatic). 
a, place where air-bladder comes in œs, cesophagus, 
contact with subopercular integu- ^ p, pad of air bladder. 
ment. sp. c, Spinal cord. 
br. c, branchial cavity. v. 1, centrum of atlas vertebra. 
ly, lymphatic gland (so called head-kidney). : 
