On the development of the vascular system in the foetus of vertebrated animals. Part 2 / by Allen Thomson.

Date:
[1831]
Catalogue details

Licence: Public Domain Mark

Credit: On the development of the vascular system in the foetus of vertebrated animals. Part 2 / by Allen Thomson. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    ferous animal, when they are removed from their ova and divest- ed of the accessory membranes; and impossible for the expe- rienced eye even, to perceive the differences between tbe embryoes of the different families of the same order, as of birds or mam- malia. The following may be regarded as some of the more important particulars in which the phenomena of development correspond in the different orders of vertebrated animals :—1. The ovum being essentially composed of a yolk, or collection of granular substance, enclosed in a membrane, along with some accessory parts, all enveloped by a general covering, to which the name of chorion may be most properly applied. 2. The existence of some part of the yolk, generally of a firmer consistence than the rest, situated towards the upper surface, and of a membranous form, called the germinal membrane, in which the changes connected with the formation of tbe foetus more immediately take place. 3. The commencement of the formation of the embryo being indicated by the appearance of a streak and small groove, in the centre of the germinal membrane, and this groove afterwards forming the rudiment of, or being converted into, the spinal canal. 4. The separation of the substance of the germinal membrane into three layers, in which different systems of the animal appear to originate. 5. The expansion of these layers of the germinal mem- brane over the surface of the yolk, so as to form a new covering for this part, situated within its proper membrane; and the development of blood, and of a vascular network on the surface of this covering or yolk-sac. 6. The development of the head, trunk, and extremities, from the outermost or serous layer, as it has been called ; the formation of the anterior and posterior extremities taking place sooner or later, according to the cir- cumstances in which development is effected, and according to the mode of life of the perfect animal. 7. The formation of the cavities destined to contain the brain and spinal cord from folds and thickenings of the same layer. 8. The development of the organs of the senses from these cavities, and their contained parts; the early appearance of the eye and ear especially. 9. The formation of the principal circulating organs, such as the heart and larger bloodvessels, from the middle, or, as it has been named, vascular layer. And, 10. The
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