. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Fig. 217. caeca of Two colic an owl. (After Pyecraft.) Hauslrum /V^yry^rY' 3. Development Mouth and anus are not essential during em- bryonic development when the body secures its nour- ishment either from the yolk mass or, in the case of mammals, from the maternal blood stream. There comes a time, however, when provision must be made to admit food into the digestive cavity from other sources. This necessity is met by the formation of two ectodermal invagi
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Fig. 217. caeca of Two colic an owl. (After Pyecraft.) Hauslrum /V^yry^rY' 3. Development Mouth and anus are not essential during em- bryonic development when the body secures its nour- ishment either from the yolk mass or, in the case of mammals, from the maternal blood stream. There comes a time, however, when provision must be made to admit food into the digestive cavity from other sources. This necessity is met by the formation of two ectodermal invaginations, one near each end of the elongated archenteron, which break through to make a continuous open passage-way, the digestive tube (Fig. 117). The anterior ectodermal ingrowth is called the stomodaeum, and the posterior ectodermal part, the proctodaeum, while the endodermal region between them, which was originally the archenteron, is now termed the mesodaeum. The embry- onic stomodaeum stakes out the claim for the future mouth region; the proctodaeum locates the anus. The food tube thus con- sists of three embryonic components, al- though the landmarks that separate them from each other are obliterated in the adult. 4. Histology A cross section of the digestive tube within the body cavity shows it to be made up of several concentrie layers of cells (Fig. 219). The innermost layer, or mucosa, the original embryonic endoderm, is supported by mesodermal connective tissue, the submucosa. The mucosa is. Glandula Epiploica Fig. 218. Haustra of the large intestine of man, with small per- itoneal pockets, glandulae epi- ploicae, attached to the outside of the intestinal wall. (After Cunningham.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Walter, Herbert Eugene, b. 1867; Sayles, Leonard Perkins, 1902-. New
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