Lect. IX.] HOW THE BONES GROW. 227 



living building. The very term " building," which we can scarcely 

 avoid using, conveys unconsciously a wrong conception of the process ; 

 a better idea of the process is gained by saying, that we are nature's 

 husbandry, vegetative productions, developed in her great garden. 



Let us suppose now that the future Man is an inch long, and just 

 beginning to lose the quasi-larval form, and to stop up those terrible 

 " scars " in the neck, the old fishy gill-clefts, the stigmas of ancestral 

 lowliness. Along the line, where the skeleton is being developed, the 

 cells are crowded, and soon these gatherings together of a special kind 

 of protoplasmic centres become cartilage — hyaline cartilage, a substance 

 that is somewhat elastic, and is like a solid sort of cheese. When 

 this tissue has been formed by the deposit of a semi-solid substance 

 between the cells, then we have a marvellous little model of the 

 skeleton that is to be ; as yet, however, there is no bone. Let us 

 take that one little rod that is to be the thigh bone of the Man — 

 &s large as his flute — but now not more solid nor thicker than 

 the filaments inside a flower. It is all hyaline cartilage at pre- 

 sent, and the substance between the cells is in a very small 

 quantity ; yet the number of the centres of life — the protoplasmic 

 masses — goes on increasing rapidly. This small, primary thigh- 

 skeleton has this formative energy (nisus formativus) within it; 

 but it must have an incessant, never-failing supply of food, and of 

 fresh materials in the form of other species of protoplasmic cells, 

 from without. The food, of course, is the plasmic or nourishing 

 part of the blood, which is now developed, and for the containing and 

 conveying of which proper vessels, and the heart itself, have been 

 formed in connection with the other parts of the embryo. The fluid 

 which is conveyed by, but escapes through, the vessels bathes 

 ■every tissue, distilling itself like the dew of the morning upon and 

 into every growing organ. The little masses of protoplasm that 

 surround the young cartilaginous femur, or thigh-skeleton, are most 

 important factors in the formation of this and the other organs of 

 support. The cortical part forms a bark of fine fibres, like the 

 "bast" or flax-layer in the stalk of the islant, — it is called the 

 perichondrium — that which invests the cartilage. After a while, 

 a most delicate ring of bone forms round the little rod of cartilage, 

 between it and its bark of fibrous tissue; this is formed by the con- 

 version of the innermost layer of that investment into bone-cells 



