244 



PR A CTJCAL ANA TO. !/ ) '. 



In reality there is no difference except an arbitrary one. Each is of peri- 

 toneal origin ; each has two layers ; each escorts vessels and nerves to organs. 

 Omenta connect organ to organ ; mesenteries connect organ to wall. 



28. Usage arbitrary, 



The broad ligament holds the liver to the diaphragm ; the broad ligament ot 

 the uterus holds the uterus to the lateral pelvic walls and floor. They are the 

 mesenteries of these viscera. Usage, however, restricts the use of the word mesen- 

 tery exclusively to the intestines. As you will see, the ascending colon lost its 

 mesentery. The descending colon lost its mesentery, except the rectum, in part, 

 and the sigmoid. The transverse colon retained its mesentery. 



29. Define incsentcric attachment primitive a/id acquired. 



By primitive attachment of the mesentery we mean attachment in the mid- 

 line, or nearly in the original line of the straight gut. The mesentery of the small 

 intestine is, for practical purposes, an example of primitive attachment ; the rectum 

 is primitive in attachment. The duodenum, stomach, and colon have acquired 

 attachments. 



jastro-hfjiafc omen 



FIG. 173. DIAGRAMS SHOWING (A) THE FORMATION OK THE GREAT OMENTUM, AND () THE ROTA- 

 TION OF THE INTESTINAL CANAL. 



30. Wliat is differentiation of the alimentary canal and its pliysiological signifi- 

 cance ? 



In the evolution of the alimentary canal, differentiation is the process whereby 

 the primitive straight gut undergoes a change which determines large and small 

 intestines. The ileo-caecal junction is the place where this change took place. 

 (Fig. 172.) The physiological significance seems to be simply a physiological 

 division of labor, whereby the small intestine is specialized for digestive purposes, 

 the large intestine for disinfecting, deodorizing, storage, and extrusive purposes. 



3 1 . What is rotation f 



It is the process by which the upper border of the small intestine (Fig. 173) 

 is turned from you, from left to right, and. brought out toward you under the 

 arch of the transverse colon (Fig. 173), so as to be, when completely turned, as 

 figure 173. In figure 172 both large and small intestines have a common con- 

 tinuous mesentery, as you see. In figure 173 they still have the same mesen- 

 tery, with this difference : that for the small intestine is twisted on itself one-half 

 around. The pivot about which this rotation took place is seen in figure 172 

 the superior mesenteric artery. Examine figure 172 and see the jejunum. Trace 

 this down to the caecum. 



