DEVELOPMENT OF EAR AND ACCESSORY ORGANS IN FROG. 545 
the stapes, and in the membrane connecting it with the re- 
mainder of the capsule, a small isolated piece of cartilage is 
present. This ultimately becomes the inner end of the colu- 
mella, called by Professor Parker the interstapedial element. 
From this cartilage a thin rod of cells extends forwards and 
outwards close to the inner side of the thymus, till it ends just 
in front of the last-mentioned organ. This rod will ultimately 
be Professor Parker’s mesostapedial cartilage, and by later 
growth it will expand against the tympanic membrane at its 
distal end. At the period under consideration it is very thin 
and not easy to trace, but notwithstanding this I feel sure that 
it has no connection with any skeletal element except the 
interstapedial. Under these circumstances it is fair to assume 
that it either grows outwards from the interstapedial cartilage, or 
else, with less probability, that it is formed in situ by the scat- 
tered cells in the vicinity aggregating into the form of a bar. 
The position of the columella at this period is diagrammatically 
represented in fig. 14. It will be seen that it is not at present 
in connection with the tympanic cavity or annular cartilage, 
which are indeed far away, nor does it reach the outer surface 
of the head by some distance. It is also directed much more 
directly forwards than it is in the adult. 
Until metamorphosis takes place this state of things remains 
practically unaltered except by slight growth on the part of the 
organs involved; but as the frog leaves the water the columella 
rotates with its base as pivot, so that it comes to point more 
outwards. At the same time the mandibular and hyoid arches 
move back, as do the tympanic cavity and annular cartilage. 
This movement brings the end of the columella into close rela- 
tion with the ventral surface of the quadrate cartilage near its 
point of articulation with the capsule, and an attachment takes 
place between the two by means of a thin connecting bar, the 
suprastapedial. During this period the columella grows rapidly 
in length and increases in thickness throughout its whole extent. 
This causes the distal end to extend close over the tympanic 
cavity and to come in contact with the annular cartilage very 
shortly after the frog has completely lost its tail. At the same 
