582 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. 



limits between the longitudinal muscular layer and the inner- 

 most fasciculi of the levator ani, in consequence of their mutual 

 approximation, can no longer be distinguished. The longitudinal 

 muscular layer and the innermost fasciculi of the levator ani 

 radiate out into numerous cords, which penetrate between the 

 fasciculi of the musculus sphincter externus in such a way that 

 the ring of the sphincter externus is split into a series of 

 concentric zones ; these traverse its whole thickness, and finally 

 terminate in thin tendons, which are lost in the skin of the 

 buttock. 



The circular muscular layer at the beginning of the rectum 

 still possesses a considerable thickness. In adults it measures 

 somewhat less than one millimeter, and in the newly born child 

 about O2 of a millimeter; but it increases in proportion as the 

 anus is approximated ; it forms also temporary thickenings in 

 the lowermost plicae sigmoidese, where it interweaves with the 

 longitudinal muscular layer, receives numerous muscular fasciculi 

 from the levator ani, and finally near the anal orifice augments 

 to a thickness of five millimeters in adults, and of 0'5 of a milli- 

 meter in the newly born child, causing an annular thickening 

 termed the sphincter internus. The upper margin of this ring 

 is by no means sharply defined, whilst if a longitudinal section 

 be carried through the lowermost part of the rectum, the thick- 

 ening caused by the sphincter internus is seen to be club-shaped. 



Immediately below the sphincter internus, and situated 

 somewhat more externally, the striated fibres of the sphincter 

 externus begin to make their appearance, forming circles round 

 the anal opening, and laterally blending with the most external 

 fasciculi of the levator ani. 



Mucous MEMBRANE. The mucous membrane of the lower 

 part of the rectum in man usually presents valve-like pro- 

 cesses, running at right angles to the axis of the intestine, but 

 usually extending over only a portion of the circumference. 

 They are neither incapable of obliteration, nor invariably pre- 

 sent, though the muscular tissue enters into their formation. 

 In the great majority of cases I found them to be three or four 

 in number, of which one, and indeed usually the lowest, ap- 

 peared so far independent that a thickening of the circular 



