126 



ANIMAL PHYSIOLOGY. 



[LESSON 36. 



580. The mouth in the higher Crustacea is generally furnished 

 with a pair of strong palpigerous mandibles, and five or more pairs 

 of jointed under jaws, which move transversely, and support articu- 

 lated feelers ; the three outer pairs of under jaws are the largest, and 

 support gills at their base. 



581. The entrance of the mouth presents an upper lip, a bifid 

 tongue, and sometimes an under lip. The mouth opens by a very 

 short, narrow ossophagus into a capacious stomach (Fig. 207), pro- 

 vided internally with a great number of minute (microscopical) 

 teeth; in addition to these, there are three very large calcareous 

 teeth, situated near the pyloric orifice of the stomach, their external 

 portion being remarkable for their redness. 



In examining the external aspect of this stomach, the very short 



FIG. 207. FIG. 208. 



External view, stomach of Lobster. 



Stomach of Lobster opened to show 

 gastric teeth in situ. 



oesophagus (b) is seen to terminate immediately in the capacious di- 

 gestive sac (d), at the upper portion of which a pair of short, strong 

 jaws (c) are seen. A number of strong calcareous bones, longitudinal 

 in their direction, support the membranous portion of the stomach, 

 and form a solid basis for the support of the large teeth. The cen- 

 tral rounded tooth (5, Fig. 208) is supported upon a large, somewhat 

 triangular bone, transverse in its direction. The entire organ is cov- 

 ered externally with a layer of muscle's of great power. The pylo- 

 rus is shown at a (Fig. 207). 



582. Two of these teeth (a, Fig. 208) resemble the grinding or 

 molar teeth of an Elephant, whilst the third, which is placed in 

 front, and somewhat below the former, has a rounded termination (b\ 

 The lateral teeth are employed to cut, divide, and comminute the 

 food, which is performed by a rounding motion, like the action of 

 one mill-stone upon another; the third tooth is employed in constant- 

 ly pushing the food, as it escapes between the grinding teeth, back 

 again, to be more thoroughly triturated. 



