1 662 



HUMAN ANATOMY. 



specimens, is as follows: average of upper segment 25 mm., of lower 33 mm. 

 The largest pair was an upper of 37 mm. and a lower of 44 mm. ; the smallest of 

 12 mm. and 3 mm. respectively. The last, perhaps, was pathological ; the next 

 smallest was 14 mm. and 19 mm. We have seen a caecum with the upper seg- 

 ment entirely wanting. The absence of both has been observed. The average 

 length of the ileo-caecal opening on 30 similar specimens was 31 mm., the extremes 

 being 46 mm. and 21 mm. It is probable that, owing to the shrinking of the tissues, 

 these dimensions of the opening are excessive. Although the lower fold is the 

 larger, the upper overlaps it almost invariably, so that when the valve is closed the 

 two edges do not come in contact, the orifice being closed by the application of the 

 lower fold to the under surface of the upper one. Inflated specimens show that 

 the upper fold is tense, while the lower remains flaccid. Much difference of 

 opinion exists as to the completeness of the closure of the ileo-caecal valve, and 

 experiments do not agree. If the experiment of injecting water or air from the 

 colon be performed in situ, the closure is more likely to be perfect than if the parts 

 have been removed. These experiments, however, do not represent the true con- 



FIG. 1414. 



Ascending colon 



Anterior band- 



Cecu 



Ileo-caecal artery 



Superior ileo-caecal fossa 



Mesentery 



Meso-appendix 

 Vermiform appendix/ 

 Caecum and related structures seen from the left. 



Appendicular artery 



ditions during life, since the tonicity of the muscular fibres of the gut is lost, and, 

 in the opened abdomen, the pressure of the viscera on the end of the ileum is less 

 than normal. In life the valve probably is efficient. 



The orifice of the vermiform appendix is very variable. In some cases 

 the caecum narrows to it so gradually that it is hard to say where it begins ; in 

 others it begins suddenlv with an oval or round opening measuring from 5 mm. or 

 less to i cm. or more. The va/:'<- which often is found at the orifice is not usually 

 a true valve, but the projection made by the wall at the union of ca-cum and appen- 

 dix in the entering angle when it arises obliquely. According to Struthers, there is 

 no valve when it arises at right angles. Owing to its usual upward course, the fold 

 is most often on that side when present. YVe have seen a true valve as a small 

 independent fold; usually, however, there is no effective guard to the entrance of 



the appendix. 



Position. The ca-cum is situated in the right iliac fossa, resting on the iliac 

 fascia covering the ilio-psoas muscle, above the outer part of Poupart's ligament, 



