THE MECHANISM OF THE GIZZARD IN BIRDS. 105 
15. ON THE MECHANISM OF THE GIZZARD IN 
BIRDS.* 
Notwitustaxpine the fact that the external form and general Page 525. 
structure of the gizzard is known to almost every one, very little seems 
to have been. made out as to the means by which this organ is 
enabled to crush and render available for nutrition the hard grains 
taken as food. 
By most writers the gizzard is supposed to act as a grinding-mill, 
moving from side to side, assisted in its work by sharp-pointed stones 
which its owner swallows for the purpose. This was evidently the 
opinion of Hunter, though he seemed scarcely satisfied on the point 
when he found that there was no perceptible lateral movement of 
the muscular masses during digestion. 
Harvey gave a very good description of the action of the gizzard, 
as far as he knew it, in his description of the abdominal viscera of 
the common fowl (“On Generation,” Exercise vii); and Hunter is 
the only physiologist who seems to have worked at the subject since 
that time. 
The structure of the gizzard as a specialised organ is best seen in 
the Anserine birds; and that of the Goose will be now described. 
Externally it is circular when looked at from in front, oval from 
the side, and fusiform from above or below. The cesophagus enters 
it as a large infundibuliform tube, with the broader end downwards 
at its highest point; and the duodenum is continued ont of it behind Page 526. 
and above. 
The organ may be shown to consist of two lateral masses of 
muscle, with an oblong cavity between them, which opens above and 
below into two sacs, with muscular walls of nearly uniform thickness. 
The anterior superficial circular view presents the appearance of a 
central tendinous area, from which four lines radiate, nearly at right 
angles to one another, in an X-like manner. The upper and lower 
median areas between the corresponding limbs of the X are muscular 
and rounded at the margin, with the fibres directed to the central 
tendon. The lateral spaces are covered with glistening tendon, which 
at the edges shades into muscular fibres, not in this case curved, but 
straight and consequently squared off. 
The superior and inferior median portions are parts of the walls of 
* “Proceedings of the Zoological Society,” 1872, pp. 525-9. Read, April 16, 
1872. 
