A system of obstetrics . on of the valve as to allow of the continued passageof venous blood, especially when the circulation is disturbed by over-exertion, from the right to the left auricle, as occurs in the malforma-tion [causing] the morbus coeruleus. The Visceral Arches and Clefts.—Closely connected in developmentalhistory with the aortic arches are certain structures known as the vis-ceral, or branchial, arches and clefts. These are primarily four pairs ofslits on the sides of the neck, which in fishes and many amphibia remainthroughout life as the gill-clefts extending from the exterior
A system of obstetrics . on of the valve as to allow of the continued passageof venous blood, especially when the circulation is disturbed by over-exertion, from the right to the left auricle, as occurs in the malforma-tion [causing] the morbus coeruleus. The Visceral Arches and Clefts.—Closely connected in developmentalhistory with the aortic arches are certain structures known as the vis-ceral, or branchial, arches and clefts. These are primarily four pairs ofslits on the sides of the neck, which in fishes and many amphibia remainthroughout life as the gill-clefts extending from the exterior surface tothe pharyngeal cavity. According to recent investigations, these slitsare imperfect in the embryos of existing birds and mammals, beingclosed by a thin membrane. The first to appear is the most anterior,and the others follow in regular order: in a human embryo of threeweeks three pairs of the gill-clefts are present, and very soon the fourthappears (Fig. 121, A). The front edge of each cleft grows out into a. (From Quains Anatomy, after Ecker.) A, from a human embryo of about three weeks: 1, cere-bral vesicle or developing cerebral hemisphere; 2, the inter-brain or diencephalon; 3,frontal process; 4, superior maxillary plate; 5, eye; 6, inferior maxillary plate; 7, secondbranchial arch ; 8, third; 9, fourth : posterior to each of these is the corresponding visceralor branchial cleft. B (from an embryo of about five weeks): 1, 2, 3, 5, as in A; 6, superior maxillary plate; 7, infe-rior maxillary; 8, outer part of first cleft, which becomes the external auditory meatus. Beneath 3 in A is seen the aperture of the stomadaeum. prominent ridge, the visceral or branchial arch, as does ultimately theposterior edge of the hindmost slit: there are therefore five arches oneach side. The aortic arches run at first in the corresponding branchialarches. In man the clefts very soon are obliterated (during the secondmonth) except the first, of which the external auditory meatus, t
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectobstetrics, bookyear1
