GASTRIC GLANDS OF THE MAKSUPIALIA. 7 



longitudinal bundles (fig. 1, musc.l.) are external and the trans- 

 verse ones (musc.t.) internal. But many are cut obliquely, and 

 over the area occupied by the gastric gland (i. e. almost the 

 whole of the lesser curvature) the oblique and longitudinal 

 bundles form the greater part of the muscularis. Mixed with 

 these striated muscle bundles there are strands of plain muscle 

 fibres (PI. 1. fig. 3, mp.), the number and masses of which diminish 

 towards the oesophagus. Striated muscle fibres are found over 

 the region of the pyloric glands, and indeed form the muscu- 

 lature of the gastric-gland thickening. Delicate strands of both 

 plain and striated (PI. 1. fig. 3, m.int.) muscle fibres penetrate 

 into the submucosa, between the secondary tubules of the gland, 

 although most of these are anstriated fibres, and are derived 

 probably both from muscularis and muscularis mucosae. 



The course taken by the secondary tubules or involution of 

 the gastric gland is, in Phascolomys, a comparatively simple one. 

 Many openings on the surface of the gland lead into simple pits, 

 but others are more complex, and a single tubule divides into a 

 small number (2-6) of branches. But the length of these side 

 tubules relatively to their diameter is much less than in Phasco- 

 larctus. The lumen is always a narrow one ; and the thickness 

 of the epithelium lining these tubules is generally greater than 

 that on the free surface of the stomach. 



Phascolaectus. 

 The most striking differences in the structure of the gastric 

 gland of the Koala and that just described for the Wombat, lie in 

 the greater compactness of the former and greater complexity in 

 the ramifications of the tubules, and in the nature of the muscular 

 coat. The latter is arranged in an external longitudinal (PL 1. 

 fig. 2, musc.l.) and an internal circular layer (musc.t.). But the 

 musculature over the gastric gland, which in Phascolomys was 

 composed predominantly of striated fibres, is here made up entirely 

 of nonstriated fibres (Pi. 1. fig. 4, musc.l., musc.t.). The muscu- 

 laris is less strongly developed than in Phascolomys, and the 

 transverse bundles are the more numerous. At the oesophagus 

 striated muscle fibres (PI. 1. fig. 2, m.oe.) are present; and the 

 transition from these to plain fibres is, on the pyloric side of the 

 oesophageal opening, a sharp one. On the cardiac side, however, 

 the longitudinal musculature of the oesophagus extends for a short 

 distance unmixed with nonstriated fibres over the surface of 



