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The Twentieth Century
Published in Arturo Castiglioni, A History of Medicine, 2019
After completion of gastrulation the results of exchange transplantations are quite different. At these later stages the fate of various regions has been determined. Thus a presumptive eye region, if placed in the belly wall, becomes an eye, not skin or muscle. The fate of the presumptive mesoderm in the dorsal lip of the blastopore is determined first. Warren Lewis observed that if it is transplanted to a region of presumptive epidermis it does not form skin, but sinks beneath the surface, where it may produce somites or a notochord (1907). The experiment was repeated by Spemann and Mangold (1924) with one important difference: if early gastrulae were used as hosts, instead of Lewis’s older larvae, the fate of the transplant was similar to that observed by Lewis, but the response of the host was very different. Now the overlying ectoderm produced a neural plate, and in some instances a secondary embryo.
Integrin Function in Early Vertebrate Development: Perspectives from Studies of Amphibian Embryos
Published in Yoshikazu Takada, Integrins: The Biological Problems, 2017
Mechanistically, the process of gastrulation may be considered on several levels that include: (1) the “behavior” of the individual cells that collectively serve to “drive” morphogenesis at gastrulation, (2) the molecules mediating the shape changes and adhesive properties of these cells, and (3) the control of the timing and patterning of the cellular movements involved. Following the progression through early cleavage and blastula stages, gastrulation begins with the appearance of a slit-like invagination of bottle cells, termed the blastopore, on the dorsal side of the embryo as illustrated in Figure 1. The involuting mesoderm subsequently comes in contact with the blastocoel roof and travels along it in the direction of the animal pole. The zone of involution initiated at the dorsal lip of the blastopore spreads laterally and ventrally to enclose the endoderm, which remains visible as a yolk plug through late gastrulation. The superficial cells of the animal pole and equatorial marginal zone spread by epiboly during this process, thus covering the entire outer surface of the embryo. Inside the embryo, the endodermally derived archenteron forms as the mesoderm advances, resulting in the displacement of the blastocoel (Figure 1).
Experiences with Osteoligamentoplasty According to Weiss for the Treatment of Scapholunate Dissociation
Published in Journal of Investigative Surgery, 2018
W. Petersen, J. Rothenberger, H. E. Schaller, A. Rahmanian-Schwarz, M. Held
Subsequently, quadratic troughs, of roughly equal size to that of the bone blocks previously harvested in both the scaphoid and the lunate, were excised using a micro-sagittal oscillating saw and a chisel (Figure 7C). Subsequently, the autograft bone block, previously harvested from the distal radius, was placed into the scaphoid and lunate troughs using digital pressure (Figure 7D). The graft was fixed further in the receiving area using periosteal and transosseous sutures to ensure stabilization. The wrist was then slightly distracted and brought into about 30° of extension, effectively locking the autograft into both the scaphoid and the lunate, using the dorsal lip of the distal radius. The capsule was repaired with some slight imbrication to allow pressure over the dorsal aspect of the wrist joint.