THE LARGE INTESTINE OF THE PIG 493 



tern already discussed. At the same time the apex will advance 

 from a to 6. This has happened in the 120-mm. embryo (fig. 

 12), and accordingly 3| revolutions are there present. The 

 same is true of the coil from a pig four weeks after birth (fig. 

 13). Gradually the spiral becomes more compact and its coils 

 more adherent to one another, and at the same time the portions 

 of the inner coil which are visible on the exterior become buried. 

 These changes are clearly shown in the figures. In the adult 

 (fig. 14) the apex of the coil has rotated so that instead of point- 

 ing downward, it is directed toward the left, and thus four 

 revolutions are completed. Less of the inner coil is exposed 

 than at birth, and only half a turn can now be observed at the 

 apex. With these relatively slight changes in the constitution 

 of the coil, its general appearance has been transformed through 

 the development of the sacculations, which at birth are scarcely 

 indicated. 



The principal morphological feature of the developing coil 

 which the figures fail to suggest, is its increase in size and much 

 greater increase in length. This can be shown by measurements; 

 and at the same time the position of the apex can be more ac- 

 curately located. The following table, therefore, includes the 

 total length of the spiral part of the colon (from the cohc valve 

 to the contact with the duodenum), and also the distance from 

 the colic valve to the apex of the coil. The apex in the earlier 

 stages is temporary, and in the 95-mm. specimen (fig. 9) it 

 must be chosen somewhat arbitrarily. When the distance from 

 the colic valve to the apex of the coil has reached 50 per cent 

 of the length of the entire spiral, the permanent apex has pre- 

 sumably become estabhshed. Accordingly, in the table, the 

 distance to the apex is followed by the percentage, which it 

 represents, of the spiral part of the colon. Measurements of the 

 small coils are made with some difficulty, so that the results 

 are only approximately correct; but even with these limitations, 

 the measurements are found instructive. 



