20 DR. E. LciNNBERG ON DIGESTIVE [Jan. 14, 



ti'ansversely in the colon as the latter is apt to do, but longi- 

 tudinally, so that one plica extends down the colon, the other in 

 an opposite direction on the other side. I am, however, inclined 

 to think that these plicse morphologically correspond to the more 

 or less developed casco-colic valve of other related forms. Although 

 the direction is different the connection with the ileo-cfecal valve 

 may decide in favour of such an interpretation. These plicae do 

 not form any boundary between the ctecum and the colon. They 

 form no boundary at all directed as they are now. But how 

 could they get such a direction ? I tliink this may be explained 

 in connection with the shape of the c^cum. Owen, in describing 

 the intestine of the Wombat, used the following words : — " The 

 ca?cum is extremely short but wide ; it is remarkable for being- 

 provided with a vermiform appendage." ' Later authors have 

 adopted this same interpretation, biit I hardly think it is right. 

 If it had been a true vermiform appendage, that is, the reduced 

 blind end of a ca?cum, it ought to have opened into the ctecum of 

 which it itself was a part. But it does not, as has been already 

 stated above. It opens with a quite independent opening of its 

 own near that of the ileum. I judge from this that the so-called 

 processus vermiformis of the Wombat rejrresents a rudiment of 

 the whole ccecum. If we assume that a moderately developed 

 cfecum should for some reason or another become reduced to a 

 mere appendage, it must acquu'e a similar situation and open into 

 the colon close to the ileum. It might then easily happen that 

 the wall of the terminal portion of the rudimentary ca?cum 

 became fused with the wall of the ileo-ca?cal valve. Such an 

 event might be the more easily effected as the shortened 

 mesentery of the ccecal rudiment woidd draw the latter more and 

 more to the ileum and make both more closely connected. It 

 would also be more convenient if the two openings into the colon 

 lay near each other and were parallel in direction, because there 

 would then be less risk of particles of food entering the ca?cal 

 rudiment. I believe, indeed, that such a retrogi-ade development 

 has really taken place, and that in the ancestors of the Wombat 

 the ca?cum has been reduced to a rudiment, which might happen 

 if they lived on such a diet that the CtTCum was not needed for 

 the digestion of the food. When the Cfecum had ah'eady reached 

 a considerable degree of reduction, the diet of the animals was 

 changed, and they began by-and-bye to feed on harder and less 

 easily digestible vegetable matter containing cellulose, etc. The 

 Cfecum was now, however, so rudimentary that it could not, as in 

 other related forms which live on a similar diet, help in the 

 digestion of this food-stuff. This function became, therefore, the 

 duty of the colon alone, which in consequence had to be con- 

 siderably enlarged. It grew in strength, and its capacity increased 

 so that it would be able to hold the gTcatly augmented amount of 

 the less nourishing food that was needed for the sustaining of life 

 and gro^Hh. The colon was then distended by the large quantities 

 ^ Owen : ' Anat. of Vertebr.' p. 417. 



