THE SONG OF FISHES. 
349 
superior, and i its posterior inferior border. It is pierced by an 
elliptical foramen,/, m t. Median tendon, representing a kind 
of “ racbis ” or mid-rib of tbe entire apparatus. 
Fig. 4. Transverse section of tbe air-bladder of tbe same fisb. ra, la. 
Right and left appendicular lobes, m m. Cavity of tbe prin- 
cipal lobe, m t. Median tendon, i m. Tbe two “ intrinsic ” 
muscles of tbe air-bladder. Tbe oblique direction of tbeir 
fleshy bundles of fibres can be seen. 
Figs. 5, 6, 7. Various phases of development of tbe air-bladder of tbe 
same fisb. Tbe lettering as before. 
Fig. 8. Right lobe of tbe air-bladder of tbe Dactylopterus (Z). volitans ), 
represented in section to show tbe incomplete diaphragm (d), 
which projects at tbe level of tbe tubular isthmus (c) of com- 
munication with tbe left lobe, rl, pa. Internal surface of main 
cavity, and (< pyramidal appendix” of right lobe respectively. 
