I 



COMPARATIVE ANATOMY 35 



bulging internally into the lumen. This may be called 

 the caecal tonsil and is characteristically present in the 

 slightly developed caeca of carnivora. 

 It is seen in : — 



The Dog (Canis Familiaris), 

 The Cat (Felis Domestica), 

 The Lion (Felis Leo), and others. 



Clasfi B. — The development of the lymphoid appen- 

 dix is a further elaboration. The apical portion of the 

 caecum tapers gradually or, in its highest modifications, 

 is of uniformly small bore being sharply demarcated 

 from the rest of the caecum. 



It' is interesting to observe that the lymphoid tissues 

 in the fauces and in the caecum each present themselves, 

 dt one time as a bulging mass, at. another time, as a 

 blind tube. (Fig. 6.) 



The vermiform appendix is of far more widespread 

 occurrence than is generally recognised.* It attains its 

 maximum size and complexity in the rodents, which 

 also exhibit the highest development of the caecum. 



A well-developed vermiform appendix (or to avoid 

 disputes as to terminology, a caecal apex with reduced" 

 lumen but with lymphoid tissue in its walls) is to be 

 found in the following species : — 



Most rodents, e.g., Rabbit (Lepus Cuniculus), Fig. 23; 

 Hare; Lagomys PusilluSf't Fig. 8; Beaver (Cas- 

 tor Fiber), Fig. 9 ; Canadian Porcupine (Ery- 

 thrizon Dorsatus), Fig. 10. 



* At the Royal Society of Medicine in 1916 the following mis-siate- 

 ment : "No mammals other than man have a caecal appendix except 

 apes " occurred in a paper read before the Pathological Section. 



t This animal possesses two adenoid vermiform appendages, one 

 close to the ileum and the other at the apex of the caecum. Some 

 rodents present two lymphoid areas in the caecum, one immediately 

 beyond the ileo-caecal sphincter, the other at the apex of the caecum. 

 Anparently in this animal both areas have become converted into 

 blind tubes. 



