|
|
| (32 intermediate revisions by the same user not shown) |
| Line 1: |
Line 1: |
| {{Header}}
| | #REDIRECT [[Paper - Observations on the neural crest of a ten-somite human embryo (1939)]] |
| Baxter JS. and Boyd JD. Observations on The Neural Crest of a Ten-Somite Human Embryo (1939) J Anat. 73:318–326. PMID 17104759
| |
| | |
| [[Historic Embryology Papers]] | |
| {{Historic Disclaimer}}
| |
| ==Observations on The Neural Crest of a Ten-Somite Human Embryo==
| |
| | |
| By J. S. Baxter And J. D. Boyd
| |
| | |
| | |
| In the course of a study of a ten-somite human embryo in a good state of preservation we observed an unusual arrangement of those neural crest cells which form the acoustico-facial primordium. This led us to investigate the arrangement and distribution of the whole of the neural crest, and, as there are few detailed accounts of the neural crest in human somite embryos, we present our results as a separate contribution.
| |
| | |
| | |
| The embryo was obtained by laparotomy from a case of tubal gestation. The clinical history suggests that, if ovulation occurred about the mid-point of the menstrual cycle, the conceptional age of the embryo is approximately 28 days.<ref>We are indebted to Dr H. T. Laycock of Addenbrooke’s Hospital, Cambridge, for the opportunity of studying this specimen. Details of the clinical history of the patient from whom the embryo was obtained will be given in a subsequent contribution.</ref> When received in the laboratory the intact chorionic vesicle had been fixed in formalin (of unknown strength) for several days. In its longest axis the vesicle measured 14 mm., in its shortest 12 mm. Having been dissected from the main part of the chorion, the embryo, with the connecting stalk and the adjacent chorionic wall, was stained in bulk with alum cochineal, dehydrated by the drop method, imbedded in paraffin and cut transversely at Sp. into a complete series of sections. The sections were then stained on the slide with orange G.
| |
| | |
| | |
| A number of reconstructions of this embryo have been made. Those of interest for the purpose of this description are a wax-plate model of the external form of the embryo, anda millboard-wax model (according to the method of Green, 1937), of the cranial portion of the nervous system and its associated neural crest primordia.
| |
| | |
| | |
| The sectioned embryo, and the reconstructions, show that the neural folds have united from a point somewhat cranial to the otic placodes to the level of the seventh somite. Here the closure of the neural tube is discontinuous, and the caudal extremity of the neural plate is a thickened, flattened area of columnar cells continuous laterally with the somatic ectoderm. The appearance of this caudal portion of the nervous system is very similar to that presented by other human embryos at a comparable stage of development. The cranial extremities of the neural folds, however, are not widely separated and thus contrast with the condition usually found at this stage. The anterior neuropore is, then, a narrow, deep cleft (Pl. I, figs. 1, 2); and, in our opinion, it is quite possible that this appearance may be ascribed to undue shrinkage of the embryo during fixation. There is a certain degree of asymmetry in the state of development of the two sides of the neural primordium, the right side of the central nervous system being more advanced than the left. This asymmetry has been described in a number of human somite embryos (cp. Bartelmez & Evans, 1926).
| |
| | |
| | |
| There are three regions in our embryo in which neural crest cells are found in relation with the developing nervous system (see Text-fig. 1). The most anterior of these regions is at the level where the cranial flexure is most pronounced, and here, on either side of the open neural folds, there is a discrete mass of neural crest cells. The right one is better developed and will be described first.
| |
| | |
| | |
| | |
| | |
| Text-fig. 1. Geometric projection of the right profile view of a reconstruction of the cephalic portion of the nervous system. The various primordia of the neural crest are shown. The hatched line indicates the margin of the left neural fold. The arrow shows the cranial limit of the first somite.
| |
| | |
| | |
| It is, obviously, the crista neumlis rostralis of Bartelmez & Evans, or the
| |
| craniale Kopfganglienleiste of Veit (1919). Although, caudally, there is a small
| |
| isolated portion of this neural crest material, we do not think that a distinct
| |
| subdivision into a “pars optica” and a “pars trigeminalis” is present. The
| |
| neural crest cells do, however, extend forwards to the dorsal edge of the optic
| |
| | |
| | |
| | |
| | |
| {{Footer}}
| |
