In the rabbit intestine Peyer's patches can easily be distinguished. They are 
found in the jejunum and ileum, but not in the duodenum. The highest number 
observed is seven. In most animals the first, i.e. proximally situated patch has 
a rather well-defined place in the beginning of the jejunum; similarly, the 
last, i.e. distally situated one mostly has its place in the end of the ileum. 
The demarcation of the three classical sections of the small intestine is 
discussed from a comparative viewpoint with special criticism as to what is 
called ileum in man.