THE OSSEOUS SYSTEM. 



lage, grow independently with them, but is developed by degrees, from 

 a plasma successively secreted from the vessels of the periosteum, the 

 two lamellae of which are conjoined at the margin of the ossifying 

 plate. The cells of this plasma, the metamorphosis of which, as in the 

 periosteal layers, cannot be followed in every particular, are elongated, 

 measuring in man, for the most part, 0-006-0-01 of a line, and pre- 

 senting granular contents with oval nuclei of 0*0028 0*00-18 of a line. 

 Such of these cells as are destined for the growth of the bone in thick- 

 'ness, with the exception of those of the glenoid cavity of the temporal 

 bone, never present the slightest resemblance to cartilage-cells, and, 

 together with their matrix, invariably ossify without the appearance of 

 any calcareous particles ; those on the borders or extremities, on the 

 contrary, may, as it appears, subsequently, take on the nature of true 

 cartilage. The most striking example of this kind occurs in the con- 

 dyle of the inferior maxilla, where, even during foetal life, a thick car- 

 tilaginous layer is deposited, which so long as the growth of the bone 

 continues, precedes its longitudinal growth, exactly like an epiphysal 

 cartilage. I have noticed the same thing in the articular fossa of the 

 temporal bone, where, however, the cartilage is less developed ; at the 

 angle of the inferior maxilla (in the Calf), and at the anterior extremi- 

 ties of each half of the same bone, which are connected by a semi- 

 fibrous, semi-cartilaginous substance, corresponding very nearly with 

 the symphysis. This fact loses much of the singularity which at first 

 sight attaches to it, when we consider that all cartilage is at first soft, 

 and consists of common formative cells. It is, consequently, only ne- 

 cessary that the formative cells of the soft blastema of the secondary 

 bones, should, at a certain period, pass through the same changes as 

 those undergone by the formative cells of embryonic cartilage, in order 

 to effect the production of cartilage in the bones. now in question. 

 Further investigation is required to show, whether cartilage of this 

 kind also occurs as a supplementary addition to other secondary bones, 

 and to what extent, in animals. Still, it may be noticed, that in 

 asserting as I have done, that all ossifications from a soft blastema 

 take place without the deposition of calcareous granules, this statement 

 is only in part correct, because it is quite true, in many cases, that this 

 sort of deposition does occur in them, though never at an early period, 

 and, generally speaking, but rarely. The ossifying margin, moreover, 

 in these cases is never abrupt, as it is in ossifying cartilage. 



The ultimate changes of the secondary bones have not yet been 

 closely investigated. Their mode of connection with each other, and 

 also with primary bones by suture and coalescence, is tolerably well 

 known. In the vault of the cranium, for instance, as the primary 

 ossific points first appear in the situation of the tuberosities of the 

 parietal and frontal bones, the bones are at first placed widely asunder, 



