34 COMPARATIVE ANATOMY. 



what complicated arrangement of calcified bars and plates. It 

 is divided transversely by a rather deep fissure into an anterior 

 layer or cardiac portion, and a posterior smaller or pyloric 

 division. The structure of the calcified gastric skeleton is as 

 follows. 



Crossing the stomach transversely, at the hinder border of 

 the cardiac division, is a broad and slightly arcuated plate, the 

 ' cardiac ossicle.' Attached to each extremity of this 'cardiac 

 ossicle ' is a curved triangular ' ptero-cardiac ossicle/ On each 

 side a large elongated ' supero-lateral ossicle/ wider posteriorly 

 than anteriorly, is connected with the lower end of the ' ptero- 

 cardiac ossicle/ and passing upwards and backwards articulates 

 by the anterior part of its hinder extremity with a small 

 transverse rod, which forms the medial part of the anterior 

 boundary of the pyloric portions, and is termed the ' pyloric 

 ossicle/ The posterior part of the superior extremity of the 

 ' supero-lateral ossicle ' is connected with a triangularly shaped 

 imperfectly calcified plate, the ' meso-pyloric ossicle/ An- 

 teriorly this ossicle becomes continuous with the hinder edge 

 of the pyloric ossicle. " These pieces, it will be observed, form 

 a sort of hexagonal frame whose anterior and lateral angles are 

 formed by moveable joints, while the posterior angles are 

 united by an elastic meso-pyloric plate." From the middle 

 of the cardiac piece a strong calcified process passes downwards 

 and backwards underneath the ' meso-pyloric ossicle/ termi- 

 nating in a broad thickened extremity, which may be termed 

 the post-cardiac process, and to which is attached internally a 

 broad and flat chitinous plate. This plate has its postero- 

 lateral and internal angles slightly nodular. These nodules 

 represent the cardiac teeth of the Common Cray-fish. A very 

 narrow and uncalcified band connects the end of the post-cardiac 

 process with a broad calcified process, the ' uro-cardiac ossicle/ 

 This ossicle carries on its inferior surface a strong conical tooth, 

 which projects into the cavity of the pyloric divisions of the 

 stomach. Finally, connected in a similar manner with the end 

 of the uro-cardiac piece, is a broad somewhat triangularly 

 shaped ossicle, convex above and concave beneath, the 'pre- 

 pyloric ossicle/ This passes upwards and forwards, and connects 

 the uro-cardiac with the pyloric ossicle. In A the greater 



