314 



EXCRETION 0$ F^CAL MATTER. 



1 



2 

 Fig. 129. 



The Perinseum and its Muscles 1, Anus ; 2, coccyx ; 3, tuberosity ; 4, sciatic 

 ligament ; 5, cotyloid cavity ; B, bulbo-cavernosus muscle ; Ts, superficial 

 transverse perineal muscle ; F, fascia of the deep transverse perineal muscle ; 

 J, ischio-cavernosus muscle ; M, obturator internus ; S, external anal sphinc- 

 ter ; L, levator ani ; P, pyriformis (Henle). 



dogs with the posterior roots of their lower lumbar and sacral nerves divided, 

 the anus remained open, and not unfrequently a mass of faeces remained half 

 ejected. As the sensibility of the rectum and anus was abolished in these animals, 

 the sphincters could not contract reflexly, nor could there be any voluntary con- 

 traction of the sphincters. 



The external sphincter can be contracted voluntarily from the cerebrum^ 

 like any voluntary muscle, but the closure can only be effected up to a 

 certain degree. When the pressure from above is very great, the energetic 

 peristalsis at last overcomes the strongest voluntary impulses. Stimula- 

 tion of the peduncles of the cerebrum and of the spinal cord below this 

 point, causes contraction of the external sphincter. 



Defaecation. The evacuation of the faeces, which in man usually occurs 

 at certain times, begins with a lively peristalsis of the large intestine, 

 which passes downwards to the rectum. In order that the mass of 



