DIGESTION 299 



inches. That leading to the colon is situated above the ileo- 

 C8ecal opening, so that the contents are passed to the colon 

 against gravity. 



The large colon is more than double the capacity of the 

 caecum. The diameter near the csecum is only two to three 

 inches, but it increases rapidly to nine or ten in the ventral 

 portions. At the pelvic flexure the diameter becomes reduced 

 to three or four inches but rapidly increases, to reach a 

 maximum of as much as twenty inches in the right dorsal 

 colon, which narrows down like a funnel to join the small 

 colon. The small colon has a diameter of three to four 

 inches. The csecum and the ventral portion of the large 

 colon have four longitudinal bands of muscle — tsenia — and 

 four rows of sacculations. The small colon has two bands 

 and two rows of sacculation. These sacculations increase the 

 surface area. According to F. Smith, irregular contractions 

 of the muscular bands produce displacements and distorsions 

 of the colon which are causes of "colic" to which the horse 

 is so liable. 



Supplementary Structure. — (1) The salivary glands have 

 been described (p. 293). 



(2) The Liver is a large solid organ, formed originally as a 

 double outgrowth from the alimentary canal. Each of these 

 outgrowths branches repeatedly, and the blood coming from 

 the mother to the fa?tus flows in a number of capillary 

 channels between the branches. Later, when the alimentary 

 canal has developed, the blood from it is streamed between 

 the liver tubules. The fibrous tissue supporting the liver 

 cuts it up into a number of small divisions, the lobules, each 

 lobule being composed of a series of obliterated tubules 

 arranged radially with blood-vessels coursing between 

 them. 



The portal vein, which takes blood from the stomach, 

 intestine, pancreas, and spleen, breaks up in the liver, and 

 carries the blood between the lobules. From the interlobular 

 branches capillaries run inward and enter a central vein 

 which carries the blood from each lobule, and pours it into 

 the hepatic veins, which join the inferior vena cava. The 

 supporting tissue of the liver is supplied by the hepatic 



