Vermiforrii Appendix. IH? 



the rabbit is lost in procession through the rodent order. With 

 such knowledge it is futile to pursue the investigation of the 

 rabbit gland further. It is entirely illegitimate to believe that 

 the rabbit's caecal lymphoid gland should make its appearance 

 in the vestigial vermiform appendix of man or of the wombat. 



Neither in external appearance nor in structure is there a 

 likeness between the vermiform appendix of the wombat (Fig. 7) 

 and the caecal end of the rabbit. Anatomists cannot accept 

 each of these animals as the possessors of vermiform appendices 

 unless they deprive the word of all sense and meaning. 



A likeness has been seen by Mitchell in working out the 

 lymphoid theory between the caecal end of the rabbit and the 

 vermiform appendix. The lymphoid gland in the rabbit's caecal 

 end causes such an upheaval of the mucous membrane that the 

 lumen of the caecal end of the rabbit becomes narrowed to such 

 an extent that its digestive function is reduced to a minimum 

 or altogether ceases. On opening a rabbit's caecum this area 

 of caecum is often found empty of ingesta, whilst the remainder 

 of the caecum is distended with ingesta. The sole likeness of 

 the rabbit's caecal end to the vermiform appendix lies in the 

 fact that both canals are narrowed in the lumen and conse- 

 quently are of little account as digestive organs. In evolu- 

 tionary changes the rabbit is remotely removed from that stage 

 of caecal involution at which a vermiform appendix becomes 

 jjossible. (Fig. 8. B.) If lymphoid tissue is to take the place of 

 shape in naming the end of the caecum, the rabbit's caecal end 

 represents the truest type of vermiform appendix. The vermiform 

 appendix was named before a,ny thought was given to its con- 

 tained lymphoid tissue. Since histologists mistook lymphoid 

 cells for shape the rabbit's caecal end lias been erroneously 

 called a vermiform appendix. 



The shape of the appendix depends on the nnisciihir wall oj the 

 caecieni, the oi/tstandino cause i>ein!^- the external longitudinal muscle 

 coat arranged in bands over tvhat is regarded as the caecum, and in 

 a sheath or sac over that part of the caecum ivhich is called the 

 veriniforin appendix. (Figs. 2 and 7.) 



Surgeons guide themselves to the appendix by following the 

 longitudinal muscle bands. Morphologists nmst, in order to 

 tmderstand the force which compels the characteristic shape of 

 the appendix, also follow the longitudinal muscle bands. 



