THE DIGESTIVE ORGANS. 



137 



peritoneum which partially envelops the organs that are contained 

 in the abdominal cavity. Where this serous covering is wanting 

 the external coat consists of areolar fibrous tissue, which serves to 

 connect the organs of the digestive tract with neighboring struct- 

 ures, and thus becomes continuous with the areolar-tissue system 

 pervading the whole body. It supports the vessels and nerves 

 which make their way through it to the different organs. 



In addition to the organs above enumerated, it is appropriate to 

 consider here the structure of the tongue, pharynx, salivary glands, 

 and pancreas. 



1. The tongue consists chiefly of voluntary muscles, the fibres of 

 which are grouped in bundles running in various directions through 

 the substance of the organ. Between the individual striated mus- 

 cle-fibres, and also between the bundles into which they are col- 

 lected, there is a variable amount of areolar fibrous tissue contain- 

 ing fat, nerves, and bloodvessels (Fig. 67). This areolar tissue 



Fig. 114. Fig. 115. 



Sections of papillae of tongue. 



Fig. 114.— Filiform papillae ; human. Heitzmann.) 



Fig. 115.— Fungiform papilla ; human. (Heitzmann.) 



E, stratified epithelium ; C, injected capillaries within the fibrous tissue of the papilla; ; 



L, lymphadenoid tissue in lower portion of mucous membrane ; M, muscular tissue of 



the tongue. 



is more abundant near the surface of the tongue, and is covered 

 with a layer of stratified epithelium, thicker at the sides and on the 

 dorsum of the tongue than on its under surface, where it becomes 



