﻿208 Proceedings of the Royal Physical Society. 



bone development, published in Piersol's Human Anatomy^ 

 Lippincott & Co., 1907, which possesses the merits of being 

 authoritative and recent. 



(a) The Histology of Endochondral Bone Develoipment. — 

 "The primary cartilage, formed by the proliferation and 

 condensation of the elements of the young mesoblastic 

 tissue, gradually assumes the characteristics of embryonal 

 cartilage which, by the end of the second month of intrauterine 

 life, maps out the principal segments of the foetal carti- 

 laginous skeleton. These segments are invested by a 

 primitive form of perichondrium or primary periosteum^, 

 from which proceed the elements actively engaged in the 

 production of the osseous tissue. The initial changes 

 appear within the cartilage at points known as centres of 

 ossification, which in the long bones are situated about the 

 middle of the future shaft. These early changes involve 

 both cells and matrix which exhibit conspicuous increase 

 in size and amount respectively. As a further consequence 

 of this activity, the cartilage cells become larger and more 

 vesicular, and encroach upon the intervening matrix in 

 which deposition of lime salts now takes place. 



" On acquiring their maximum growth, the cartilage cells 

 soon exhibit indications of impaired vitality as suggested 

 by their shrinking protoplasm and degenerating nuclei. 



" Coincidentally with these intra-cartilaginous changes, 

 a thin peripheral layer of bone has been formed beneath 

 the young periosteum ; from the latter bud-like processes 

 of the osteogenetic layer grow inward from the periphery, 

 and invade the embryonal cartilage ; by absorption of the 

 cartilage matrix they gain the centre of ossification, and 

 there effect a destruction of the less resistant cells and 

 intervening matrix. In consequence of the penetration of 

 the periosteal processes, and the accompanying absorption 

 of the cartilage, a space, the primary marrow cavity, now 

 occupies the centre of ossification, and contains the direct 

 continuation of the osteogenetic layer. This tissue, the 

 primary marrow which has thus gained access to the 

 interior of the cartilage, contributes the cellular elements 



