DIGESTION. 



131 



It is chiefly concentrated bile with intestinal epithelium. The color- 

 ing matter is a mixture ol' hilirubin and biliverdin, not stercobilin. 

 Defecation. The act of defecation is, to a slight extent, volun- 

 tary, being in the in a in, involuntary, .hi order that the faeces may 

 not stimulate mechanically the sphincter reflexes so that they relax 

 at any time, volition plays a role. For there is a center, having its 

 seat in the brain, which is inhibitory, and by voluntary impulses the 





Fig. 37. Inhibitory Apparatus of Ano-spinal ("enter. 



A, H, Locus niger of Cerebral crura. E, F, Inhibitory fibers. P, Pons. 

 M, Medulla oblongata. C, C, Sensory fibers. 8, Ano-spinal center. 



individual is capable of relaxing or increasing the contraction of the 

 external sphincter ani. 



The inhibitory apparatus of the ano-spinal center arises, accord- 

 ing to the latest researches that I have made upon the subject, from 

 the locus niger of the crura cerebri. From this point inhibitory 

 fibers descend, some of which commence to decussate at a point in 

 the pons down to the nib of the calamus scriptorius, and then pass 

 down the lateral columns. Some of the fibers, not decussating, also 

 pass down the lateral column. This inhibitory apparatus is under 

 the control of a center in the cortex. I might add here that the 

 same inhibitory apparatus presides over the sphincter vaginae. 



