MR. SIBSON ON THE BLOW-HOLE OF THE PORPOISE. 
121 
Porpoise. The adjustments of the apparatus are such that the animal can close or 
open the outer passage either above or below the anterior pouches. When the 
outer passage is closed, the posterior pouches can be distended and the anterior are 
emptied ; and when the passage is open, the anterior pouches can be distended and 
the posterior are emptied. 
The pouches evidently serve to buoy up the head, so that when the Porpoise rises 
from the deep, the opening for breathing comes first to the surface ; and if the animal 
remains at the surface, either in sleep or in the act of coition, the air in the pouches 
will float the blow-hole above the level of the water, when the whole body of the 
animal is below the level. 
The Porpoise, I believe, does not spout. The blow-hole of the whale is in principle 
the same with that of the Porpoise. I was led, some years since, to think, from the 
examination of a Rorqual, that the spouting of the whale consists in the regurgita- 
tion from the stomach of the sea- water that it must swallow plentifully with its food. 
I was induced to form this opinion from noticing the direction of the first stomach, 
which may be described as an expanded pouch of the oesophagus, and which is so 
placed as to send its contents, when it is contracted, directly upwards through the 
oesophagus, provided the communication be open, and the form of the larynx boat- 
shaped below, and capable of being completely closed. 
Apart from all speculation, the blow-hole of the Porpoise, forming a part of its 
mechanism of respiration, must in itself be regarded as one of the most intricate and 
nicely adjusted apparatus that has yet been observed. 
Description of the Plate. 
PLATE XII. 
Fig. 1. (Must be looked at, not in the direction of the plate, but sideways.) It re- 
presents the cranium of the Porpoise, a section of the blow-hole or nasal 
canal, and the sacs. 
Fig. 2. The cranium of the Porpoise with the muscles that close and open the blow- 
hole, and also those acting upon and emptying the sacs. 
Fig. 3. A section of the pharynx and of the naso-pharyngeal canal leading from the 
larynx to the nostrils, exhibiting the larynx. 
Besides the engraved figures there are five others, deposited in the Archives of the 
Royal Society, exhibiting, in various stages of their dissection, the muscles that act 
upon the sacs and the passages of the blow-hole. 
The same numbers refer to the same parts in all the figures. 
Nos. 1.1. Figs. 1.2 (figs. 4.8. Archives of the Royal Society). The two anterior supe- 
rior lateral sacs. Membranous. 
MDCCCXLVIII. 
R 
