44 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



4. The fate of the hypomere. — The cavity of the hypomere is the coelom 

 of the adult. The splanchnic walls of the hypomeres of the two sides fold 

 around the archenteron and give rise to mesenchyme, from which are pro- 

 duced the smooth muscle and connective-tissue coats of the digestive tract, 

 and also the smooth muscle, connective tissue, cartilage, etc., as the case may be, 

 of all the derivatives of the digestive tract mentioned above. The hypomere 

 also gives rise to the linings of all the coelomic cavities, the serosa of the viscera, 

 and all of the mesenteries. The splanchnic mesoderm of the hypomere produces 

 the heart. In the region of the gill slits the hypomere produces voluntary 

 muscles. 



5. The products of the mesenchyme. — The mesenchyme gives rise to all 

 of the connective tissues of the body, including cartilage and bone; to all of the 

 involuntary or smooth muscles; to the blood cells, the blood vessels, the lymph 

 vessels, and lymph glands; and to the voluntary muscles of the appendages. 

 It has already been stated that the vast majority of the mesenchyme is of meso- 

 dermal origin, but a small part arises from the other germ layers. 



