Vermiform Appendir. 357 



vermiform appendix is developed for lymphoid tissue. With 

 this lymphoid theory swept away the older and correct theory 

 remains established. The vermiform appendix is the vestige of 

 a larger ancestral caecum. Practically it has no function, its 

 small size denoting loss of function by atrophy. 



The appendix is a rare form of caecal involution which is due 

 to the peculiar arrangement of the external muscle coat of the 

 caecum (longitudinal bands on the caecum terminating in a 

 muscle sheath on the vermiform appendix). 



DESCRIPTION OF PLATES LXVI.-LXXVa. 



1. Wombat (Phascolomys mitchelli). Caecal area showing 



vermiform appendix. 



2. Human vermiform appendix. 



3. Rabbit's caecum showing pseudo-vermiform appendix. 



4. Section of rabbit's caecal end showing massed lymphoid tissue 



5. Section of human appendix showing lymphoid tissue. 



6. Section of kitten's caecum showing lymphoid tissue sur- 



rounding the mucosa. 



7. Wombat (Phascolomys latifrons). Caecal area showing 



vermiform appendix. 



8. Treves' four types of caecum. 



9. Outlet of appendix into caecum. 



10. Baboon's caecum showing bands terminating at apex of 



caecum. 



11. Lemur's caecum showing bands terminating in muscle sheath. 



12. Foetal caecum, human. 



13. D type of caecum showing U-shaped muscle band resulting 



from distension following atrophy. 



14. Intestines of wombat. 



15. Undifferentiated intestinal tract of Tasmanian devil 



(Sarcophilus). 



16. Human caecum like a wombat's caecum. 



17. Section of wombat's caecum. A. Solitary lymphoid nodule. 



18. Section of wombat's caecum. A. Solitary lymphoid nodule. 



19. Koala's caecum. 



20. Young wombat's caecal area showing appendix. 



21. Caecal area, ileum, vermiform appendix, and colon. Flin- 



ders Island wombat (Phascolomys ursinus). 



