160 



ESSENTIALS OF ZOOLOGY 



wall of the stomach to help digestion by churning and mixing the 

 food with digestive juices. At the posterior end a pyloric valve in 

 the form of a sphincter muscle guards the entrance to the small 

 intestine which follows. This is the convoluted intestine which is 

 divided into the anterior duodenum, middle jejunum, and posterior 

 ileum. Its walls produce digestive enzymes from glands and it re- 

 ceives digestive juices from two other glands: the liver and the 

 pancreas. 



■Craniom 

 Skull ^ ^^^tm^mr^ Orbit 



Cervical 

 y/erfebrae 



Scapula 



Mandible 

 Clavicle 



Sternum 



Thoracic 

 vertebrae 



Lumbar 

 vertebrae 



Sacrum 



Metacarpals 



Tibia 



Metatarsals 



Humerus 

 Rib 



Pelvis 



Radius 

 Ulna 

 Carpals 



Hcvnct 



Fig. 52. — Human skeleton. 



(From Wolcott, Animal Biology, McGraw-Hill Book 

 Company, Inc.) 



The digested food is taken up by the lymphatic spaces and by 

 blood vessels which are embedded in the wall just outside of the 

 lining epithelium. The liver is the largest organ in the body of 



