528 MR. A. H. GARROD ON THE GIZZARD OF BIRDS. [Apr. 16, 



them, into which the seeds and stones are thrust by the simul- 

 taneous contraction of the superior and inferior muscular bags. 

 Directly these have become fully contracted, the lateral muscles 

 act ; and by approximating the anterior and posterior tendons they 

 become greatly expanded laterally. But this expansion can take 

 place in one direction only — namely, towards the gizzard-cavity ; for 

 the anterior and posterior tendons being situated obliquely with 

 regard to one another, and the contraction taking place through the 

 whole mass, expansion can only occur towards the base of the 

 triangle. The motion in this direction is furthered by the arrange- 

 ment of some of the muscular fibres, as can be seen on close inspec- 

 tion of the section of the relaxed gizzard ; for the dense horny 

 pads above referred to are cupped on their attached surfaces, and 

 the fibres run from one margin of this cup to the other, in an arched 

 manner, as seen in the section. Those fibres just above the cup are 

 arched also in the same way, and the epithelial margins of the cup 

 are more yielding than elsewhere. Consecjuently, when the con- 

 traction occurs, the fibres straightening reduce the antero-pos- 

 terior diameter of the cup and make the pad more convex towards 

 the intermediate cavity, and push each towards its fellow, this 

 action, combined with that of the other more marginal fibres, pro- 

 ducing a most powerful compression of the contents. 



The great force exercised laterally by the contraction of a muscle 

 can be well shown by tying a piece of tape round the middle of the 

 arm proper, and then causing the biceps to contract forcibly, 

 whereby the tape is broken. 



As remarked by most writers on the subject, every intermediate 

 condition of muscularity of stomach may be found in birds, from 

 the simple non-tendinous one of the Raptores and others to the 

 most muscular of the Anserine birds. The degree of muscularity 

 depends on the nature of the food which the bird obtains, as shown 

 by Hunter's experiment, in which he, by giving animal food to a 

 Duck (I believe), caused a great diminution in the muscularity of its 

 gizzard. 



The state of the bird as to health also influences the development 

 of the muscular fibres, the heart and gizzard being very similarly 

 affected by impaired nutrition. 



In the Gallinaceous and Passerine birds there is seldom a callous 

 pad formed over the lateral muscles, the epithelium being generally 

 plicated at right angles to the direction of the muscular fibres ; and 

 in them the organ seems to be a more simple squeezing-organ, 

 though when rigor mortis occurs in a contracted gizzard it is seen 

 that the muscular masses are convex on their opposed faces. 



From these remarks and what has been previously observed on 

 the subject, the following summary statement may be made : — 



The gizzard is an organ which crushes, and so renders assimilable 

 the harder portions of the food of birds. This food, having been 

 previously macerated in the proventriculus or crop, is thrust between 

 the lateral muscles (where it gets mixed with the small sharp stones 

 it meets there) by the contraction of the superior and inferior 



