350 Stapley and Leivls : 



takuble evidence of complete atrophy having occurred. Because 

 complete atrophy of the caecum has occurred in the marsupial 

 order, accompanied by appendicular formation, the Australian 

 order stands alone in value for the comparative study of the 

 caecum. 



Briefly considered, marsupials afford three most interesting 

 types : — 



(1) The koala (Phascolarctus cinereus) (Fig. 19), with a huge 



caecum. 



(2) Th,e wombat with a caecum represented by a true 



vermiform appendix (Fig. 7). 



(3) The Tasmanian devil (Sarcophiiu.s satanicus (Fig. 15) 



without a caecum. 



Tlie Carnivora throw a strong sidelight on caecal variations. 

 No muscle bands form on the caecum, consequently caecal 

 atrophy occurs in those animals without the formation of a 

 vermiform appendix. The hyena has fair caecal development. 



The mongoose has an atrophic caecum which would show a 

 vermiform appendix had the arrangement of the longitudinal 

 bands been suitable ; but it has no vermiform appendix. 



The Himalayan bear has no caecum. Thus in the mongoose 

 a small caecum occurs without muscle bands ; in the bear caecal 

 atrophy has proceeded to completion. Considering the three 

 orders, Primates, Marsupials and Carnivora, we are able to 

 definitely state that three stages of caecal atrophy are possible. 



1. — With an ajjpendix, resulting from the external muscle 

 coat forming bands on the caecum, and a muscle sheath on the 

 appendix. (Man, Fig. 2 ; wombat, Figs. 14, 1, 7.) 



2. — Without an appendix, the muscle bands terminating at 

 the apex of the caecum. (Fig. 10.) Baboon. 



3. — Without an appendix and without muscle bands, as in the 

 mongoose or the domestic cat. 



The variations of the external muscle coat explain the infrequency 

 with ivhich caecal atrophy is accompanied by the formation oj a 

 ver7nijorm appendix. 



The dog is of great interest because its caecum is distorted by 

 peritoneal adhesions. About the distortion of the dog's caecum 

 and the appendix of man a common cause operates, viz., 

 peritoneal adhesions. As both man and dog are irregular and 



