THE CECUM. 



1661 



FIG. 14.13. 



Anterior band 



Ascending colon 



ternally and somewhat posteriorly. From the top of the ileum a deep furrow passes 

 posteriorly partly around the gut, and a less marked one is found in front. 

 Although starting as just stated, the furrows at once descend a little, so as to repre- 

 sent truly the middle of the orifice. These serve as an external boundary between 

 the caecum and the colon, which are much alike in general characters. The average 

 length of the caecum in the adult is between 6 and 7 cm. (about 2^ in.), and its 

 breadth about 8 cm. (3^ in.). 1 The bands of the colon are continued onto the 

 caecum of the adult, and terminate at the origin of the appendix. One band is in 

 front and the other two externally and internally at the back. The parts between 

 the bands are generally expanded pouches, which may be subdivided by horizontal 

 constrictions. There are two chief forms of caecum with several minor modifica- 

 tions : the first is a persistence of 

 the foetal type, in which the caecum 

 has the shape of a cornucopia bent 

 towards the left, with the tapering 

 end continued as the vermiform 

 appendix ; the other, which is the 

 usual, and occurs in from 91-94 

 per cent, of adults, is due to the 

 part between the external and the 

 anterior band growing out of all 

 proportion, so that the pouch be- 

 tween them becomes the lowest 

 part, apparently the apex, the ap- 

 pendix arising from the internal 

 posterior side near the ileum. In 

 extreme cases the two may be very 

 close together. Very rarely the 

 caecum is symmetrically sacculated, 

 with the appendix at the lower end. 

 To understand the interior 

 of the caecum it must be remem- 

 bered that the end of the ileum is 

 thrust in at the angle between the 

 colon and caecum in such a way 

 that originally in fcetal life all the 

 coats were involved. The serous 

 coat is replaced by areolar tissue 

 where two layers come together 

 and new longitudinal muscular 

 fibres are subsequently developed 

 which do not enter the folds ; how- 

 ever, the original longitudinal mus- 

 cular layer, as well as the circular 

 one, does .so. The latter is thick- 

 ened inside the fold. The ileum, 



as it approaches its end, lies between the surface of the caecum below and the lower 

 swelling of the colon above ; thus the upper of the two lips of the elliptical opening 

 is composed of colon and ileum, the lower of ileum and caecum. They form promi- 

 nent shelf-like projections into the large gut, opposite the external furrows, and 

 constitute the ileo-csecal valve (valvula coli). The folds meet at the ends of 

 the opening, forming single continuations or retinacula, of which the posterior is 

 much the larger. It often extends across the posterior to the lateral aspect of the 

 gut. The two segments converge, but at different angles. The upper, slanting 

 somewhat downward, is approximately horizontal, while the lower is more nearly 

 vertical. The orifice of the ileum between these folds is elongated when the gut 

 is distended, the posterior end being sharper than the anterior. The diameter of 

 the segments, measured from the origin to the free edge on 35 inflated and dried 



1 Berry : The Anatomy of the Caecum, Anat. Anzeiger, Bd. x., 1895. 



Ileum 



Caecum 



Opening of 

 appendix 



Beginning of large intestine, somewhat inflated ; part of an- 

 terior wall removed to show ileo-caecal valve and orifice of vermi- 

 form appendix. 



