IO4 MORPHOLOGY OF THE ORGANS OF VERTEBRATES. 



(mesenteries, in the broader sense of the word) which connect 

 the various viscera to the walls of the body cavity. The condi- 

 tions in the abdominal region will be described first. 



Here the splanchnic layer of the mesothelium applies itself 



to either side of the 

 walls of the alimen- 

 tary tract, it being 

 8 of course kept in 

 mind that mesenchy- 

 matous tissue has 

 migrated in between 

 entoderm and meso- 

 thelium in this re- 

 gion (see p. 103), 

 while above and be- 

 low the digestive 

 tract the dorsal and 

 ventral walls of the 

 hypomere press in- 

 wards towards the 

 median line, insinu- 

 ating themselves 

 dorsally between the 

 alimentary canal and 



FIG. 113. Diagrammatic section of vertebrate ' 



through abdominal region, a, dorsal aorta; c, coelom; 

 g, gonad ; gl, glomerulus ; i, alimentary canal ; /, 

 liver; m, mesentery; MU, muscular layer of myotome; 

 my, myoccele ; n, nephrostome ; na, neural arch ; nc, 

 notochord ; o, omentum ; s, spinal cord ; so, somatic 

 layer of peritoneum ; sp, splanchnic layer of peri- 

 toneum ; /, nephridial tubule ; vm, ventral mesentery ; double Partition be- 

 w, Wolffian duct. 



tween the metacceles 



of the two sides both above and below the intestine, with a 

 small amount of mesenchymatous tissue between the two epi- 

 thelial walls. These partitions, which thus come to support 

 the alimentary canal (Fig. 1 1 3), are the dorsal and ventral 

 mesenteries. 



The ventral mesentery is never perfect throughout the 

 abdominal cavity. In the posterior portion the partition walls 



the notochord, ven- 

 trally between the 

 entoderm and ecto- 

 derm. As a result 

 there is formed a 



