1 88 OSSEOUS SYSTEM. [sect. IOI. 



The cells of the cartilage are developed from the primitive embryonic cells 

 which, while they become larger, develop an interstitial substance between 

 them. The whole embryonic and subsequent growth of the cartilage, is 

 owing to the increase of this intermediate substance and the multiplication 

 of the cells (see § n). The cartilage-cells of the adult, accordingly, are the 

 descendants of the primitive embryonic-cells. 



§ ioi. Metamorphoses of the Primitive Cartilaginous Skeleton. 

 — Of the primitive cartilages, some are further developed with the 

 other portions of the skeleton, and become the permanent car- 

 tilages of the nose, joints, symphyses, and synchondroses; a few 

 disappear in the course of development (certain cranial cartilages, 

 see § ioo) ; but the greatest number finally ossify and form the 

 first rudiments of the bones of the trunk and extremities, and of 

 a considerable portion of those of the skull. All these bones 

 ossify in essentially the same manner. At one or more points 

 (puncta ossijicationis), a deposition of calcareous salts begins in 

 their interior contemporaneously with an alteration of the carti- 

 laginous elements • and this metamorphosis, advancing in some or 

 in all directions, continually converts more cartilaginous parts 

 into bone. While this takes place, the cartilage, in most cases, 

 ceases to grow in one direction, and, consequently, is soon wholly 

 converted into bone, but extends itself in Other directions, and 

 thus continually furnishes new formative material to the advancing 

 bone, and may become the seat of new centres of ossification, as 

 in the epiphyses of the cylindrical bones. Still the bone, after it 

 has invaded the whole of the cartilage, and converted its perichon- 

 drium into periosteum, does not cease enlarging; but from this 

 period to that of completed growth, a new and peculiar method of 

 formation takes place in all these places. This consists in the 

 ossification of an organised soft formative substance, situate upon 

 the inner surface of the vascular periosteum, and formed from it; 

 the ossification proceeding from the surface of the bone outwards 

 through the soft substance, which in proportion as this takes place, 

 is continually reproduced from the periosteum. 



Recent observations of H. Midler show that the first ossification in the 

 diaphyses of the long bones of the calf takes place in the outermost parts 

 of the cartilage, if not in the periosteal layer itself. The first rudiment of the 

 femur, for instance, has therefore the form of a short tube surrounding the 

 primordial cartilage. Further observation will show how the ossification 

 proceeds in this animal. The same fact had, however, been observed by How- 

 ship, in the case of the metacarpal and phalangeal bones of the human embryo, 

 and he inferred that the cylindrical bones of mammalia generally follow this 

 rule. (Medico-Chir. Trans. 1819. Vol. vi. pp. 264 and 283, and PI. i. fig. 1.) 



