A text-book of embryology for students of medicine / by John Clement Heisler. With 190 illustrations, 26 of them in colors.

  • Heisler, John C. (John Clement), 1862-1938.
Date:
1899
Catalogue details

Licence: Public Domain Mark

Credit: A text-book of embryology for students of medicine / by John Clement Heisler. With 190 illustrations, 26 of them in colors. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    by the ectoderm and the entoderm. Each arch contains an artery, the visceral-arch vessel. These five pairs of visceral- arch vessels arise by a common stem, the truncus arteriosus, from the primitive heart.^ The morphological significance of the visceral arches and clefts may be appreciated by a comparison of the conditions Fig. 50.—Coronal sections of two human embryos, showing ventral wall of pharyngeal end of gut-tract from behind (from Tourneux, after His). A, from embryo of 3.2 mm.; B, of 4.25 mm. (about 25 to 30 days). I, II, III, IV, outer vis- ceral furrows; V, sinus prsecervicalis, comprising third and fourtli outer furrows; 1, S, 3, U, visceral arches, each with its visceral-arch vessel; 6, tuberculum impar; 7, orifice of larynx; S, pulmonary evagination. obtaining in lower types. While in birds and mammals the number of the clefts is four, in reptiles, amphibians, and bony fishes, five clefts appear, and in some fishes (selachians) the number is six. In all aquatic vertebrates, the thin epithelial closing membranes rupture, thus establishing com- munications between the alimentary tract and the exterior, through which openings water ])asses in and out. The mar- gins of the clefts—except the first or hyomandibular cleft— become the seat of a rich supply of capillary blood-vessels, the blood of which obtains oxygen from the water and yields to the latter its carbon dioxid; while the visceral arches, excluding the first and second, become known in these classes as branchial arches from their producing bony arches which ' For an account of the metamorphoHis of the vi.sceral-arch vessels into the adult arteries of the throat and neck the reader is referred to Chapter X.