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



at its highest point ; and the duodenum is continued out of it behind 

 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 mus- 

 cular 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 the corresponding cavities already mentioned ; and the oesophagus 

 enters the former at its inner angle, close to its junction with the 

 right lateral mass ; the duodenum being behind. 



The lateral masses, with their tendinous coverings, are the mus- 

 cular portions ; and the cavity between them is just behind the 

 central tendon. 



The epithelial lining of the whole organ is very dense, and is 

 continuous through the different cavities, terminating abruptly at 

 the entrances to the oesophagus and the duodenum. Very shortly 

 after the death of the bird it can be stripped off entire*. It is par- 

 ticularly dense where it covers the two lateral muscles, and generally 

 forms a callous oval pad over each, which has to receive most of the 

 force of the muscular walls as they act on the stones and food. 



The central tendons, one in front and the other behind, are very 

 strong ; and so are the fibres which radiate outwards from them ; 

 they are almost entirely connected with the lateral muscles. 



The lateral muscular masses have their fibres all tending forwards 

 and backwards, each being inserted into both the front and back 

 tendinous expansion, the central being nearly straight and the lateral 

 ones being curved slightly outwards in the middle of their course. 



The superior and inferior sacs are surrounded by muscular bands 

 which bow over from front to back, being inserted into those parts 

 of the margin of the central tendon to which they are opposite. 

 By their contraction they reduce the size of the sacs and force any 

 thing they contain between the lateral muscles, a considerable fold 

 of the gizzard-lining, which acts as a kind of valve, preventing any 

 stones entering the duodenum. 



The action of the lateral muscles can be best understood by obser- 

 ving a horizontal section made through the middle of the gizzard. 



The section is fusiform and exhibits a central oblong cavity, short 

 from side to side, bounded before and behind by the central tendons, 

 and laterally by the triangular muscular masses. 



The accompanying figure and the above description show that in 



* This coat is considered by recent German authorities to be a secretion from 

 the deep glands, not an epithelium. 



