BILATERAL VAGOTOMY OF FROG 
209 
In the frog, the external respiratory acts consisting of buccal 
movements, closing of nares, expiration and inspiration or swal- 
lowing air, occur in a coordinated and orderly sequence, the buccal 
or passive movements proceeding rhythmically between the swal- 
lowing acts, so that there are several buccal movements between 
each swallowing act. This is the usual type of buccal move- 
ments exhibited in the frog although in exceptional cases there 
may be at times in certain animals a perfect synchrony between 
these movements and the actual swallowing of air (inspiration). 
It should be emphasized here, that the external respiratory mechan- 
ism of the amphibians differs from that of all other air-breathing 
animals in that the air enters the lungs under positive pressure 
due to the act of swallowing, therefore, this might indicate pos- 
sibly that the respiratory center in the medulla of this animal is 
anatomically and physiologically ' identical with the center for 
deglutition. 
The buccal or passive movements are distinct from the quick 
respiratory movements of the flanks, the latter being due to the 
act of inspiration or the swallowing of air which is preceded 
by the opening of the glottis and the escape of some air into the 
buccal cavity. This results first in a diminution in the size of the 
lungs with a corresponding falling in of the flanks which is then 
quickly compensated for by a distension of the lungs which in 
most animals show a periodicity similar to the Cheyne- Stokes 
type of breathing in mammals. 
The experiments forming the basis of this . report were made 
exclusively on the common laboratory frog (Rana pipiens). 
Healthy, vigorous animals were selected in pairs, one of which 
was kept as a control, while in the other, one or both vagi were 
sectioned in the region of the neck after anaesthesia. The deli- 
cate technique for this operation in this species of frog consists 
in making two oblique incisions through the skin on either side 
of the median line, ventral, about cm. distant and close to the 
anterior tips of the shoulders as represented by a line drawn from 
this point laterally about 1 cm. in length to a point slightly poste- 
rior and just internal to the articulation of the superior and 
inferior maxillary bones on either side. These two incisions ex- 
pose the cervical fascia on either side at its attachment along the 
anterior scapulo-clavicular borders. Few blood vessels are pres- 
ent and if the fascia is carefully separated no hemorrhage results. 
The fascial separation beyond this region now becomes very easy 
until the thin sheet of prevertebral fascia is reached which is 
