FireGarden
7th February 2003, 11:17 AM
(Just thought I'd try and get my research checked by someone who knows more than I do)
I've checked the modern description of the development of the human embryo, and here's how I fit Galen's description into the modern:
From Encart98 (My comments and Galen's stages in bold)
The implanted embryo consists of a hollow sphere, the blastocyst, containing a mass of cells, called the embryonic mass, attached by a stalk to one side of the encircling membrane. [Galen's First stage (hardly accurate, but this seems the best place to compare it to): "The first is that in which. as is seen both in abortions and in dissection, the form of the semen prevails. At this time, Hippocrates too, the all-marvelous, does not yet call the conformation of the animal a foetus; as we heard just now in the case of semen voided in the sixth day, he still calls it semen"] In a blastocyst less than two weeks old and measuring 1 mm (0.04 in) in diameter, the microscope reveals the amnion (a sac surrounding the embryo), chorion (a membrane that develops around the amnion and lines the uterine wall), yolk sac, and distinct germ layers.
In the third week a closed tube appears in which the brain and spinal cord are to develop. Another tube, folding on itself, is developing into the heart, [Galen's second stage (more accurate than his first, I think): "heart, brain and liver are still unarticulated and unshaped yet have by now a certain solidarity and considerable size"] and at about this stage a portion of the minute yolk sac is enclosed in the body of the embryo to form a part of the embryonic alimentary canal.
At the beginning of its fourth week the embryo, now about 4 to 5 mm (about 0.16 to 0.2 in) long, has the rudiments of eyes and ears, and each side of the neck shows four gill clefts. A tail is also present.
Early in the second month the buds of the arms and legs appear. The major internal organs begin to take shape, [Galen's third stage (Fits here quite well I suppose): "You will see the conformation of the three ruling parts more clearly, that of the parts of the stomach more dimly, and much more still, that of the limbs"] and in about the sixth week bones and muscles begin to form.
By the third month the embryo is recognizable as that of a primate, and is now called a fetus. [Of course, Galen's 4th stage could be placed much later in the Encarta98 article: "The fourth and final period is at the stage when all the parts in the limbs have been differentiated; and at this part Hippocrates the marvelous no longer calls the foetus an embryo only, but already a child"]
OK, foetus and embryo do not seem to be similarly defined in the two versions. (Similarly, semen seems to have a less than modern meaning). And Galen does not tell us (in this extract anyway) where the first stage takes place. His first stage is also very poor in that it says very little about the beginnings other than that it is fluid. But I think that Galen did quite well in stages two or three. Especially if you consider the size of the embryo at these stages (and the possibility that most of his observations may have been of chickens not humans!)
I'm not entirely clear on when he says that flesh forms to cover the bones. (Or if it's even accurate to say that the bones form before the flesh) And my earlier interpretation of his "three parts" being the gastrula is probably giving him too much credit. What he meant by "parts" (and especially "ruling parts") I do not know. (Maybe the "ruling parts" are the three he named: heart, brain and liver?)
That's the problem with reading incomplete or imprecise texts. Interpretation is always required.
I've checked the modern description of the development of the human embryo, and here's how I fit Galen's description into the modern:
From Encart98 (My comments and Galen's stages in bold)
The implanted embryo consists of a hollow sphere, the blastocyst, containing a mass of cells, called the embryonic mass, attached by a stalk to one side of the encircling membrane. [Galen's First stage (hardly accurate, but this seems the best place to compare it to): "The first is that in which. as is seen both in abortions and in dissection, the form of the semen prevails. At this time, Hippocrates too, the all-marvelous, does not yet call the conformation of the animal a foetus; as we heard just now in the case of semen voided in the sixth day, he still calls it semen"] In a blastocyst less than two weeks old and measuring 1 mm (0.04 in) in diameter, the microscope reveals the amnion (a sac surrounding the embryo), chorion (a membrane that develops around the amnion and lines the uterine wall), yolk sac, and distinct germ layers.
In the third week a closed tube appears in which the brain and spinal cord are to develop. Another tube, folding on itself, is developing into the heart, [Galen's second stage (more accurate than his first, I think): "heart, brain and liver are still unarticulated and unshaped yet have by now a certain solidarity and considerable size"] and at about this stage a portion of the minute yolk sac is enclosed in the body of the embryo to form a part of the embryonic alimentary canal.
At the beginning of its fourth week the embryo, now about 4 to 5 mm (about 0.16 to 0.2 in) long, has the rudiments of eyes and ears, and each side of the neck shows four gill clefts. A tail is also present.
Early in the second month the buds of the arms and legs appear. The major internal organs begin to take shape, [Galen's third stage (Fits here quite well I suppose): "You will see the conformation of the three ruling parts more clearly, that of the parts of the stomach more dimly, and much more still, that of the limbs"] and in about the sixth week bones and muscles begin to form.
By the third month the embryo is recognizable as that of a primate, and is now called a fetus. [Of course, Galen's 4th stage could be placed much later in the Encarta98 article: "The fourth and final period is at the stage when all the parts in the limbs have been differentiated; and at this part Hippocrates the marvelous no longer calls the foetus an embryo only, but already a child"]
OK, foetus and embryo do not seem to be similarly defined in the two versions. (Similarly, semen seems to have a less than modern meaning). And Galen does not tell us (in this extract anyway) where the first stage takes place. His first stage is also very poor in that it says very little about the beginnings other than that it is fluid. But I think that Galen did quite well in stages two or three. Especially if you consider the size of the embryo at these stages (and the possibility that most of his observations may have been of chickens not humans!)
I'm not entirely clear on when he says that flesh forms to cover the bones. (Or if it's even accurate to say that the bones form before the flesh) And my earlier interpretation of his "three parts" being the gastrula is probably giving him too much credit. What he meant by "parts" (and especially "ruling parts") I do not know. (Maybe the "ruling parts" are the three he named: heart, brain and liver?)
That's the problem with reading incomplete or imprecise texts. Interpretation is always required.