280 THE ANATOMY OF INVERTEBRATED ANIMALS. 



by close-set parallel ridges, which only become free hair-like 

 processes at the posterior margin of the plate, each ridge 

 giving attachment to a regular series of minute hairs. These 

 are directed inward nearly parallel with the surface, which 

 looks at first as if it were merely ruled with close-set trans- 

 verse lines, connected by still finer and closer longitudinal 

 ones. 



This apparatus constitutes the " amjDoule cartilagineux" 

 of Milne-Edwards. Behind it there is yet another infero- 

 median and two lateral setose valvular prominences, which 

 form the last barrier between the food and the intestine. 



Mr. T. J. Parker, who has recently carefully examined the 

 structure of the stomach of the Crayfish,^ finds that, besides 

 the anterior and posterior gastric and the cardio-pyloric mus- 

 cles, there are intrinsic fibres in the walls of the stomach, 

 some encircling the posterior pyloric region, others passing 

 between the hindermost accessory ossicle and the postero- 

 lateral and pyloric pieces ; these must tend to diminish the 

 cavity of the stomach, and the last-named fibres possibly 

 assist in mastication by bringing the lateral cardiac into con- 

 tact with the infero-lateral cardiac tooth. Moreover, there are 

 nine pairs of minor extrinsic muscles, of wdiich tw^o pairs pass 

 from the anterior wall of the stomach and gullet to the anten- 

 nary sternum, passing between the oesophageal commissures 

 and on either side of the azygos nerve of the visceral system; 

 three pairs pass between the side-walls of the stomach and 

 oesophagus and the mandibular sterna; a sixth pair arises from 

 the forward processes of the intermaxillary apodeme, and is in- 

 serted into the oesophagus; two more pairs arise, one from 

 the internal thickened edge of the mandible, the other from 

 the intermaxillary apodeme, and are inserted into the inferior 

 surface of the pyloric region ; and a ninth pair arises from the 

 carapace just behind the posterior gastric muscles, and goes 

 to be inserted into the posterior pyloric dilatation. There 

 are also a few more inconspicuous fibres passing between the 

 oesophagus and the neighboring hard parts. All these, at 

 least when acting together, must antagonize the intrinsic 

 muscles, and dilate the stomach. 



The pyloric portion of the stomach passes into the an- 

 terior portion of the intestine, which is smooth internally, 

 and presents superiorly a cascal process, the remains, accord- 

 ing to Rathke, of one lobe of the viteliary sac of the embryo 



1 Journal of Anatomy and Pliysiohgy^ October, 1876. 



