xiii PHYLUM CHORDATA 397 



stomach. From the crop the gullet is continued backwards into 

 the stomach, which consists of two parts, the proventriculus (prvn.) 

 and the gizzard (</&.). The proventriculus appears externally like a 

 slight dilatation of the gullet; but its mucous membrane is very 

 thick, and contains numerous gastric glands so large as to be 

 visible to the naked eye. The gizzard has the shape of a biconvex 

 lens : its walls are very thick and its lumen small. The thickening 

 is due mainly to the immense development of the muscles which 

 radiate from two tendons, one on each of the convex surfaces. The 

 epithelial lining of the gizzard is very thick and horny, and of a 

 yellow or green colour : its cavity always contains small stones, 

 which are swallowed by the Bird to aid the gizzard in grinding 

 up the food. 



The duodenum (duo.) leaves the gizzard quite close to the 

 entrance of the proventriculus and forms a distinct loop enclosing 

 the pancreas. The rest of the small intestine is called the ileum 

 (Urn.) : it presents first a single loop ; then follows its greater part 

 coiled into a sort of spiral ; and lastly comes a single loop which 

 passes without change of diameter into the rectum (ret.), the 

 junction between the two being marked only by a pair of small 

 blind pouches or caeca (cce.). The cloaca is a large chamber divided 

 into three compartments, the coprodceum (cpdm.), which receives the 

 rectum, the urodceum (urdm.), into which the urinary and genital 

 ducts open, and the proctodceum (prdm.), which opens externally by 

 the anus. 



There are small luccal glands opening into the mouth, but none 

 that can be called salivary. The liver (lr.) is large, and is divisible 

 into right and left lobes, each opening by its own duct (b. d. 1, 

 1). d. 2) into the duodenum : there is no gall-bladder. The pancreas 

 (pn.) is a compact reddish gland lying in the loop of the duodenum, 

 into which it discharges its secretion by three ducts (pn. d. 1-3). 

 A thick-walled glandular pouch, the bursa Fdbricii (b. fabr.), lies 

 against the dorsal wall of the cloaca in young Birds and opens 

 into the proctodaeum : it atrophies in the adult. 



Ductless Glands. The spleen (spl.) is an ovoid red body, of 

 unusually small proportional size, attached by peritoneum to the 

 right side of the proventriculus. There are paired thyroids at the 

 base of the neck ; and, in young Pigeons, there is an elongated 

 thymus on each side of the neck. The adrenals (Fig. 1049, adr.) are 

 irregular yellow bodies placed at the anterior ends of the kidneys. 



Respiratory and Vocal Organs. The glottis (Fig. I04>0,gl.) 

 is situated just behind the root of the tongue, and leads into the 

 larynx, which is supported by cartilages a cricoid divided into four 

 pieces, and paired arytenoids but does not, as in other Vetebrates, 

 function as the organ of voice. The anterior part of the trachea 

 (tr.) has the usual position, ventral to the gullet; but further back 

 it is displaced to the left by the crop, becoming ventral once more 



