368 ZOOLOGY SECT. 



they pass over the mesotarsal joint, and by the pull thus exerted 

 the toes are automatically bent round the perch by the simple 

 action of flexing the leg. They are kept in this position while 

 the Bird is asleep by the mere weight of the body. The action 

 is assisted by a small but characteristic muscle, the ambiens, which 

 arises from the pubis, passes along the inner surface of the thigh, 

 and is continued into a long tendon which comes round to the 

 outer side of the knee, enclosed in a special sheath, and, con- 

 tinuing down the leg, joins the superficial flexors of the digits. 



Digestive Organs. The mouth (Fig. 981} is bounded above 

 and below by the horny beaks, and there is no trace of teeth. 

 The tongue (tng) is large and pointed at the tip. The pharynx 

 leads into a wide and distensible gullet (gul.) which soon dilates 

 into an immense reservoir or crop (crp.) situated at the base of the 

 neck, between the skin and the muscles, and immediately in front 

 of the sternum. In this cavity the food, consisting of grain, 

 undergoes a process of maceration before being passed into the 

 stomach. From the crop the gullet is continued backwards into 

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

 and the gizzard (giz.). 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 cceca (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 buccal glands opening into the mouth, but none 

 that can be called salivary. The liver (tr.\ is large, and is divisible 

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

 b. 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 



