The Frog 



49 



back of the tongue on the floor of the mOuth is a narrow slit called the 

 glottis ( ) leading to a tube 1 passing to the lungs, 



and directly behind the glottis, a larger opening is found, leading to 

 the oesophagus, which empties into the stomach. The stomach itself 

 is crescent-shaped, lying mostly on the left side of the body. The 

 larger anterior portion is called the cardiac end ( ), while 



the constricted or posterior portion, meeting with the intestine, is known 

 as the pyloric ( ) end. 



msnt. 



I. m. 



A. A Diagram of a Transverse 



Section Through the Ileum 



of a Frog. 



cm., Circular muscle layer; c.t., 



submucosa; ep., epithelium which 



lines the gut; l.m., longitudinal 



muscle layer; msnt., mesentery; 



per., peritoneum; rid., longitudinal 



ridges of ileum composing mucosa. 



Fig. 7. 



mmmm 



B. A Portion of the Section Shown 

 in A, More Highly Magnified. 

 b.v., Blood vessel; c.t., connective 

 tissue of mucous membrane or sub- 

 mucosa; cm., circular layer of mus- 

 cle fibres; ep., epithelium; g.c, 

 goblet cell; l.m., longitudinal layer 

 of muscle fibres; let., "lacteal" or 

 lymph vessel of the intestine; leu., 

 leucocyte or lymph corpuscle; p.e., 

 peritoneal epithelium. (After 



Bourne.) 



The first portion of the intestine, a sort of U-shaped band, is known 

 as the duodenum ( ). The several coils following 



it are the intestine proper. This intestine finds its way into a large, 

 short chamber known as the rectum, which in turn communicates with 

 the exterior through what is called the cloacal opening ( ). 



The walls of the stomach are composed of five layers (Fig. 7), the outer 

 portion quite thin, called the peritoneum; then two muscular layers, the 

 outer called the longitudinal, and the inner the circular muscle layer, 

 followed by a spongy division called the submucosa and an inner folded 

 mucous layer, the mucosa itself. This latter is made up of glands lying- 

 in connective tissue. These glands are longer at the cardiac than at the 

 pyloric end. The inner layer of the intestine, the mucosa, is considerably 

 folded and consists of absorptive and goblet cells. The urinary bladder, 

 the reproductive ducts, and the rectum open into the cloaca. 



^This tube to the lungs is a part of the respiratory system; consequently the opening, the glottis, 

 really does not belong to the digestive system, but it is mentioned here because the student will see it 

 while noting the surrounding structures and it is well for him to know all related parts of a 

 given region. 



