Mr. Home on the Gizzards 
1 86 
The muscles when dissected, are found to be composed of 
fasciculi of fibres, connected together by a loose cellular 
membrane, so as to appear like so many separate muscles 
lying parallel to each other. They all arise from the anterior 
strong flat tendon, and are inserted into that on the posterior 
surface ; as they are very numerous and require a large surface 
of insertion, part of them, on a superficial examination, 
appear to be lost on the internal membrane of the gizzard. 
These muscles by their alternate action produce two effects ; 
the one a constant friction on the contents of the cavity, the 
other a pressure upon them. This last arises from the swell 
of the muscle inwards, which readily explains all the instances 
which have been given by Spallanzani and others, of the 
force of the gizzard upon substances introduced into it ; which 
force is found, by their experiments, always to act in an ob- 
lique direction. 
The internal cavity, when opened in this distended state, is 
of an oval form ; the long diameter in the line of the body : 
its capacity nearly equal to the size of a pullet’s egg, and 
there are, laterally, ridges in the horny coat, in the long 
direction of the oval. 
When the horny coat is examined in its internal structure, 
the fibres of which it is formed, are not found in a direction 
perpendicular to the ligamentous substance behind it, but in 
the upper portion of the cavity they have a direction obliquely 
downwards, and in the lower portion obliquely upwards. 
From this form of cavity it is evident, that no part of the 
sides are ever intended to be brought in contact ; and that the 
food is triturated by being mixed with hard bodies, and acted 
on by the powerful muscles which form the gizzard. 
I 
