192 THE FCETUS. 



or five. It may be compared to some of the animalcules figured 

 by MM. Prevost and Dumas, particularly to the animalcule of the 

 dog; that is to say, one of its extremities is bulbous and rounded, 

 and the other terminates in a point: which gave rise to a belief in 

 the existence of a primitive tail in the human species. Being hol- 

 low and semi-transparent, this stock seems to be filled with a limpid 

 fluid, in the centre of which may be seen, even with the naked eye, 

 an opaque filament, of a white or yellowish tint, which represents 

 the cerebro-spinal system. 



490. Numerous observations made on very young embryos seem 

 to me to prove: that the rachis is the fundamental part of the body; 

 that it appears previously to any of the other organs; that for a 

 considerable time it exists alone; that its form does not essentially 

 differ from that which it possesses during the remainder of its intra- 

 uterine life; that for twenty days, or a little longer, the embryo is 

 neither straight nor enlarged in the middle, that the head and neck 

 constitute at least one half of its total length; that the younger it 

 is the more does its curve approach to the form of a circle; that 

 the appearances of its external circumference differ very little at 

 first from what they are at a subsequent period, while its interior con- 

 tour or concavity merits the most serious attention, on account of 

 the changes it must undergo. 



491. In fact, the organs appear in succession upon this concave 

 surface; at first the difierent parts of the face, then the limbs, and 

 between these latter the thoracic and abdominal viscera. Nothing is 

 so admirable as this development; it might be called a real vegeta- 

 tion; the lower jaw, the members, the mass that is to occupy the 

 abdomen and the breast, increase and come forwards, like buds 

 springing from the branch of a tree, or axillas of a plant. 



The spinal circle thus fills up by degrees, the forehead becomes 

 farther removed from the coccyx; the thoracic and abdominal por- 

 tions of the original stock are forced to become straighter; the 

 head remains constantly inclined upon the breast, but in such a way, 

 however, that the chin at last takes the situation previously oc- 

 cupied by the forehead. The coccyx does not retire backwards 

 until a very late period; it is moved in that direction by an ex- 

 tremely simple mechanism; to wit, the development of the pelvis 

 and lower extremities. 



492. From seeing that the lateral and anterior portions of the 

 body do not become manifest for a considerable length of time af- 

 ter the vertebral frame, I have more than once been tempted to be- 

 lieve, with MM. Tiedemann and Meckel, Serres and Geofi'roy St. 

 Hilaire, that the organic evolution really takes place from the sides 



