Page:The Works of William Harvey (part 1 of 2).djvu/518

 and extremities ; like a painter, she first sketches the parts in outline, and then fills them in with colours ; or like the ship- builder, who first lays down his keel by way of foundation, and upon this raises the ribs and roof or deck : even as he builds his vessel does nature fashion the trunk of the body and add the extremities. And in this work she orders all the variety of similar parts the bones, cartilages, membranes, muscles, ten- dons, nerves, &c. from the same primary jelly or mucus. For thick filaments are produced in the first instance, and these by and by are brought to resemble cords ; then they are ren- dered cartilaginous and spinous ; and, lastly, they are hardened and concocted into bones. In the same way the thicker mem- brane which invests the brain is first cartilaginous and then bony, whilst the thinner membrane merely consolidates into the pericranium and integument. In similar order flesh and nerve from soft mucus are confirmed into muscle, tendon, and ligament; the brain and cerebellum are condensed out of a perfectly limpid water into a firm coagulum ; for the brain of infants, before the bones of the head have closed, is soft and .diffluent, and has no greater consistence than the curd of milk.

The third process is that of the viscera, the formation of which in the chick takes place after the trunk is cast in outline, or about the sixth or seventh day, the liver, lungs, kidneys, cone and ventricles of the heart, and intestines, all become visible nearly at the same moment ; they appear to arise from the veins, and to be connected with them in the same way as fungi grow upon the bark of trees. They are, as I have already said, gelatinous, white, and bloodless, until they take on their proper functions. The stomach and intestines are first disco- vered as white and tortuous filaments extending lengthwise through the abdomen ; along with these the mouth appears, from which a continuous canal extends to the anus, and con- nects the superior with the inferior parts. The organs of generation likewise appear about the same time.

Up to this period all the viscera, the intestines, and the heart itself inclusive, are excluded from the cavities of the body and hang pendulous without, attached as it were to the veins. The trunk of the body presents itself, in fact, like a boat undecked or a house without a roof, the anterior walls of the thorax and abdomen not being yet extant to close these cavities.