141 
muscle isapparently to assist the action of the longitudinalis linguae 
muscle in drawing the piston apparatus posteriorly. It is evident 
(figs. 22 and 24) that contraction of the former muscle must ma- 
terially assist the latter to remain contracted by constricting it an- 
teriorly. The longitudinalis linguae and pharyngeus muscles will be 
best described in connection with later figures. 
Figure 23 shows the appearance of the internally-situated slender 
muscle (AXIV) which probably corresponds to that termed by P. Für- 
BRINGER semi-anularis, though it differs in shape and other minor 
features. In Geotria this small muscle is attached dorsally to the 
under surface of the anterior dorsal cartilage, about midway between 
its midventral line and its extreme edge. It runs almost vertically 
downwards and becomes inserted into the upper anterior edge, not 
far from the middle, of the median ventral cartilage. The muscle 
is situated just internal to the spinoso-semianularis posterior. Its 
function is supposed to be to aid the closure of the hindermost part 
of the buccal cavity when it is necessary to shut this off from the 
throat cavity and pharynx on the animal fixing itself to some 
object—a suction process. 
Figure 24 represents a ventral view of three of the muscles above 
named, after the piston cartilage has been turned ventrally an then 
forwards, the hyo-hyoideus posterior muscle slit ventrally along the 
mid-ventral line and the halves turned dorsally to expose the longitu- 
dinalis linguae. The longitudinalis linguae (XXIII) is an elongated 
powerful muscle (figs. 22 and 24) possessing anteriorly a tendon nearly 
as long as itself which, after extending forwards in the mid-ventral 
line to the region of the dorsal process of the piston cartilage (D.P.P.C.), 
divides into two, each half becoming strongly inserted at a low level 
into the sides of this dorsal process on its posterior face. As already 
stated the longitudinalis linguae is surrounded anteriorly by the hyo- 
hyoideus posterior. It is very strongly attached along its mid-ventral 
border to the median region of the branchial basket and extends as 
far back as the pericardial capsule. Its function is of course the re- 
traction of the piston apparatus. In this figure there are also seen 
the two hyomandibulari-glossus muscles (X XIJ). Each of these is 
strongly attached posteriorly to the lower end of the styloid process 
(not shown in figure and then extends upwards between the pharyngeus 
muscle and the wall of the throat cavity, see also figs. 29 and 36) 
and forwards to become inserted into the outer side oft the anterior 
