224 A MANUAL OF VETERINARY PHYSIOLOGY 



Movements of the Intestines. 



The movements of the intestines are brought about by the 

 involuntary muscle composing its wall. This muscle in the small 

 intestines is arranged in two sheets in a circular and longitudinal 

 manner, while in the large intestines narrow bands of pale 

 muscle of considerable length take the place of the ordinary 

 longitudinal layer, and may be found on all parts where the tube 

 is sacculated. In fact, one function of the bands is to bring 

 about the sacculated condition of the canal, an important 

 arrangement whereby economy of space is effected with no loss 

 of surface. 



The sacculated condition of the double colon is confined 

 principally to the first,, second, and fourth portions. The third 

 portion, especially at the pelvic flexure, is free from sacculations, 

 and the fourth portion is not so liberally puckered as the first and 



From 

 Coecum 



Fig. 79. — Schematic Arrangement of the Muscular Bands on the Double 

 /jf Colon. 



The colon is supposed to be opened out into a straight tube. Bands 1, 2, and 3 



nki from the first colon to the pelvic flexure ; one of the three actually 



/comes from the apex of the caecum. No. 4 is the only band running the whole 



length of the bowel. Nos. 5 and 6 originate in the region of the third colon, 



and finally run on to the single colon. 



second. On the first colon there are four bands, on the second 

 colon there are also four, three of which disappear at the pelvic 

 flexure ; on the third portion there is only one band, while on 

 the fourth colon there are three (see Figs. 74 and 79). In 

 the large intestines the longitudinal layer of fibres is confined 

 to the muscular bands, so that the great bulk of the wall consists 

 of circular muscle only. The longitudinal bands shorten the 

 bowel, but the main work in pressing the contents along is per- 

 formed by the circular layer. The bands, in fact, are numerous 

 where the intestine is large, and reduced in number where the 

 bowel becomes smaller. This arrangement suggests that they 

 may, under suitable conditions, produce an irregularity of pull, 

 and we can see no other explanation of displacement of the large 

 intestines of the horse (a matter dealt with more fully at the end 

 of this chapter) than through the medium of these muscular 

 bands. 



