. Embryology. Embryology; Embryology; genealogy. THE 48-HOUR EMBRYO 219 infundibulum forms the posterior lobe. The section shows two divisions of the brain—the diencephalon and the myelencephalon. In the region of the pharynx the first visceral pouches extend laterally and meet the first visceral groove. A section of the mesenchyme is cut off to form a visceral arch, and the artery running through this mesenchyme is the first aortic arch. Just above the pharynx the two large vessels with some blood cells in them are the dorsal aortae. On either side of the hindbrain are the anterior cardinal v
. Embryology. Embryology; Embryology; genealogy. THE 48-HOUR EMBRYO 219 infundibulum forms the posterior lobe. The section shows two divisions of the brain—the diencephalon and the myelencephalon. In the region of the pharynx the first visceral pouches extend laterally and meet the first visceral groove. A section of the mesenchyme is cut off to form a visceral arch, and the artery running through this mesenchyme is the first aortic arch. Just above the pharynx the two large vessels with some blood cells in them are the dorsal aortae. On either side of the hindbrain are the anterior cardinal veins. The lens of the eye is a derivative of the head epidermis. Shortly after the optic vesicles make contact with the epidermis, a thickening appears. This invaginates (Fig. 137) and finally separates from the surface layer of epidermis. The resulting hollow body is the lens vesicle. The section shows many other interesting features. The floor of the diencephalon evaginates and touches the epidermis, which is somewhat invaginated. This is where Rathke's pouch opens into the stomodeum. From the walls of the pharynx the first and second visceral pouches have grown out to make contact with the ectoderm and two pairs of aortic arches and visceral arches are formed. One of the aortic arches is very close to a dorsal aorta, and in an adjacent section the two join. Anterior cardinal veins are present. The edge of the first somite shows one side of the hindbrain. A section of the 48-hour embryo taken just posterior to the lens reveals another epidermal structure, the otocyst (Fig. 138). Its development is very similar to that of the lens. Lateral to the myelencephalon two thickenings of the epidermis appear. They fold to form invaginating vesicles which later separate from the adjacent epidermis. The vesicles are called otocysts, or otic vesicles. One of the otic vesicles is touching the epidermis, and a few sections anterior to that shown in Figure 138 the cavity of the otocyst is
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Keywords: ., boo, bookcentury1900, booksubjectembryology, booksubjectgenealogy
