THE DIGESTIVE AND RESPIRATORY SYSTEM 297 



edentates, most insectivores, and bats, it frequently attains an 

 enormous size in herbivorous or graminivorous forms. In 

 certain rodents (e.g., muskrat, woodchuck), its total capacity 

 equals or exceeds that of the remainder of the alimentary 

 canal, and in the marsupial Phascoloarctus it is three times 

 the length of the body. In the rabbit it is provided with an 

 internal spiral valve ; in certain other rodents and in the higher 

 apes and man, the free end becomes rudimentary, restricts its 

 lumen, and forms a worm-like process, the processus (appen- 

 dix) vermif ormis , which, like all rudimentary organs, is sub- 

 ject to a large amount of individual variation. 



Thus in the human subject the appendix varies in length 

 between the limits of 2-23 cm., the average for an adult being 

 8-9 cm. It is longest proportionally during fetal life, its 

 length relative to that of the large intestine being i :io, while 

 in adult life it is 1 120. It is longest absolutely between the 

 ages of ten and twenty, after which it shows a slight reduc- 

 tion.* Its. status as a rudiment of slight functional value is 

 shown by the tendency towards the obliteration of its lumen, 

 a tendency which increases steadily with age.** Furthermore, 

 these two characters, reduction in length and obliteration of 

 the lumen, go hand in hand, short appendices being usually 

 solid, while large ones are apt to possess a lumen. 



The position and arrangement of the colon varies consider- 

 ably among various mammals. In man it begins low down 



*Zuckerkandl tabulated the length of the appendix in 161 bodies, 

 with the following result : 



mm mm 



17 20 2 cases. 90 100 15 cases. 



30 40 8 100 no 4 



4050 6 no 120 5 



5O 60 28 120 I3O 2 



6070 26 " 130140 I 



7080 29 " 140150 I 



8090 23 " 150160 I " 



** Wilhelm Miiller, from data obtained from 1,005 bodies dissected at 

 Jena between 1895 and 1897, found the amount of obliteration, partial 

 and total, to be as follows: (See table on p. 298.) 



