76 L. A. BORRADAILE. 



sharply marked off. The median tooth (28, PI. Ill), is large and well-developed. It is an 

 oblong plate, somewhat shorter than the urocardiac ossicle, at the hinder end of which it 

 is placed, and with concave sides. The inner surface bears a median longitudinal and four 

 or five pairs of lateral transverse ridges, of which the two hindermost are the stoutest. 

 The details vary considerably in different species'. The prepyloric ossicle (5, PI. III.) is a 

 T-shaped structure, placed vertically in the front wall of the pyloric division of the stomach, 

 i.e. in that wall which faces the hollow between the two divisions. The stem of the T 

 has concave sides and broadens considerably, where it joins the cross-piece. The latter is 

 slightly concave on its anterior side. 



The ossicles described in the foregoing paragraphs constitute the gastric mill, and, with the 

 muscles which move them, are the apparatus bj- which the food is triturated. To complete the 

 account of the skeleton of the stomach it is now necessary to mention certain less important 

 pieces, by which the organ maintains its shape, and which support internally the various tufts 

 and fringes of hairs with which it is provided. We may consider these in four groups : — 



(1) Those of the cardiac region, all of which lie in the ventral, or ventro-lateral wall. 

 They comprise the cardiac disks (described above), the post-oesophageal brushes, the cardiac side- 

 plates, the prepectinate ossicles, the combs, subdentary, pennate and inferolateral cardiac ossicles, 

 and the cardiopyloric valve. 



(2) Those on the ventral wall of the pyloric region ; comprising the auricular, anteroinferior 

 pyloric, preampullar, and posterior subampuUar ossicles. 



(3) Those at the sides of the pyloric region; comprising the anterior, middle, and posterior 

 pleuropyloric and anterior and middle subampullar ossicles. 



(4) Those in the dorsal wall of the pyloric region ; comprising the mesopyloric and uropy- 

 loric ossicles. 



Group 1. Podoesophageal brushes (29, PI. III.). A patch of hairs on each side of the stomach, 

 situate on a lobe formed by invagination of the wall on the ventral side, a little behind 

 the oesophagus. The outer opening of the invagination is surrounded by a calcitied ring. 



Cardiac side-plates (10, PI. III.). Large thickenings of the ventrolateral wall behind the oesophagus. 

 They are covered internally with tufts of hairs, especially long towards the hinder end. 



Prepectinate ossicles (11, PI. III.). Elongated plates in the side wall of the stomach, above the 

 cardiac side-plates. The fore end of each is thin and expanded and the upper edge thick- 

 ened along its whole length, but especially at the hinder end. 



Combs (30, PI. III.). An invagination of the wall of the stomach at the hind end of the pre- 

 pectinate ossicle of each side, producing internally a cushion on which are a number of short, 

 stout spines. 



Pectinate and post-pectinate ossicles are wanting. 



Subdentary ossicles (14, PI. III.). A slender bar running backward and downward on each side 

 from the zygocardiac ossicle to the fore end of the anterior subampullary ossicle, with which 

 and not with the inferolateral cardiac ossicle, it articulates. 



Pennate and inferolateral cardiac ossicles (12 and 13, PI. III.). Two slender bars running parallel 

 with one another along the line of junction of the ventral and lateral walls of the stomach, 

 which line is defined by their presence. At their hinder ends they curve upwards, in corre- 



' See Mocquard, oy. cit., p. 131. 



