Chap. IX.] NUTRITION AND METABOLISM. 179 



plied with glands, the orifices of which may be seen by careful 

 examination with a lens ; and posteriorly the gizzard, the walls 

 of which are exceedingly muscular, the fibres of either side 

 radiating from a central tendinous aponeurosis. The epithelium 

 here develops a dense horny coat. It is here in fact, and not 

 in the mouth as in the rabbit, that the food is triturated ; 

 and to aid in this grinding process the fowl swallows small 

 stones. 



The Glands. We must now briefly consider the glands that 

 minister to digestion ; first their structure, and then their products. 

 It will be necessary to confine our attention to the rabbit. 



The salivary glands of the rabbit are : (1) the parotid, lying 

 between the base of the ear and the angle of the lower jaw, and 

 opening forwards into the side of the mouth by the parotid 

 duct (Stenson's) ; (2) the sub-maxillary, lying between the angles 

 of the lower jaw, and opening forwards into the floor of the 

 mouth by the sub-maxillary duct (Wharton's); (3) the sub-lingual, 

 small, and lying along the inner side of the mandible, with many 

 ducts opening separately into the mouth ; (4) the infra-orbital, 

 lying in the antero-inferior region of the orbit, the duct of which 

 passes downwards to the mouth ; and (5) the small buccal and 

 other glands set in the mucous membrane of the lips, palate, 

 tongue, and pharynx. 



The buccal glands are simple or branched tubes lined with 

 epithelial cells, which are flattened in the duct, but columnar 

 in the deeper secreting part or body of the gland. The other 

 salivary glands are all of the racemose or branched tubular type. 

 The duct is elongated into a long tube, which divides and sub- 

 divides a great number of times, and so gives rise to a multitude 

 of branched tubes, each of which ends in a slight dilatation 

 (alveolus). The tubes and their alveoli are imbedded in connec- 

 tive tissue, and aggregated into lobules separated by connective 

 tissue septa. 



The cells which line the alveoli of the so-called serous sali- 

 vary glands, differ curiously according to the state of rest or 

 activity of the gland. After a period of rest they are large, 

 and have a markedly granular appearance, the protoplasm of the 



