DIGESTIVE TRACT. 4] 
continuous with the muscular coat of the stomach. Within the mus- 
cular coat is a layer made up of areolar connective tissue, called the 
sub-mucous coat. This contains numerous mucous glands and is sep- 
arated from the mucous membrane by a thin layer of unstriped muscle 
(muscularis mucose). The lining coat or mucous membrane, consists 
of two parts, an outer part or corium composed of areolar connective 
tissue in which the bloodvessels and lymphatics are distributed, and an 
inner part made up of stratified epithelium into which microscopic 
papillz from the corium project. 
DIGESTIVE TRACT. 
What is the general structure of the digestive tract ? 
It is a long tube, continuous at either end with the external surface 
of the body, and differing in size in different portions of its length. 
Where it lies in the abdominal cavity it is covered by a serous coat, 
the inner portion of which is fibrous, and the surface of the outer part 
is covered with a layer of delicate endothelial cells. Throughout its 
whole extent the digestive tract is surrounded within the serous coat 
by layers of involuntary or unstriated muscle, one layer running longi- 
tudinally with, and the other transversely to the long axis of the canal. 
In the muscular wall of the stomach a third layer is made out between 
the other two, in which the muscle fibres run obliquely. Within the 
muscular coat is the sub-mucous coat, composed of areolar connective 
tissue, separated from the mucous membrane by a thin layer of smooth 
muscle (muscularis mucosx). Some of the fibres of the muscularis 
mucos may run up between the glands of the mucous membrane. 
Where are the principal differences in structure of the wall of the 
digestive tract apparent ? 
In the mucous membrane. The other portions of the wall are about 
the same all the way throughout the tract. 
What is the structure of the mucous membrane lining the stomach ? 
On its free surface it is covered by cylindrical cells, between which 
open the ducts of numerous tubular glands. The gland tubules extend 
down to the muscularis mucosze and are single or branched. In the 
pyloric end of the stomach the glands and their ducts are lined with 
cylindrical epithelium. In the cardiac end the ducts are lined with 
cylindrical cells, while the gland tubules are lined with roundish or 
polyhedral-shaped cells that are finely granular. Between the cells 
lining the tubules and the basement membrane upon which they rest 
s 
