OSSIFICATION OF THE VERTEBRAE. 



19 



OSSIFICATION OF THE VERTEBRAE. 



The vertebrae in general. The ossification of each vertebra proceeds in cartilage from 

 three principal centres, one for the main part of the body, and one on each side for the arch 

 and processes, together with a small part of the body. The lateral centres appear about the 

 7th week of foetal life, that of the body very soon afterwards. From these centres the 

 ossification extends gradually, so as to form the greater part of the vertebra. The central 

 ossification does not pass, however, in the dorsal vertebra} the place of articulation of the head 

 of the rib, but leaves on each side a portion of the body which is formed from the lateral 

 ossification, and is separated up to the third year by a narrow cartilaginous interval the 

 newo-central gynchondroaii. It would appear farther, that while ossification in the arches 

 commences first in the cervical vertebras, the osseous centres of the bodies appear earliest in 

 the lower dorsal vertebrae. 



At the time of birth most of the vertebras consist of three osseous pieces, corresponding to 

 the three original centres. In the first year of infancy the laminas of opposite sides become 

 united in a number of the vertebras, but not in all. The spinous processes, remaining 



Fig. 19. OSSIFICATION OF THE VERTEBK.E. 

 (R. Quain.) 



A, foetal vertebra, showing the three primary centres ; 

 1 , 2, neural ossifications ; 3, central ossification. 



B, dorsal vertebra from a child of two years ; 1 & 2 

 are seen to have encroached upon the body at * the 

 neuro-central sy'nchondrosis, to have extended into the 

 articular and transverse processes, and to have united 

 behind in the spinous process, leaving the ends cartila- 

 ginous. 



C, dorsal vertebra at about seventeen years, showing 

 epiphyses on the transverse processes, 4 & 5, and 

 spinous process, 6, and the upper epiphysial plate of 

 the body, 7. 



D & E, parts of a lumbar vertebra of about the same 

 age, showing, in addition to the foregoing, 8, the lower 

 epiphysial plate of the body ; 9 & 10, the epiphyses of 

 the mamillary tubercles. 



cartilaginous for a time, are gradually completed by the growth of the cartilage and the 

 extension of the bone into them, and at the same time, by the ossific extension of the 

 transverse processes and other parts, the vertebras gradually attain to nearly their full size and 

 shape about the age of puberty. At different periods subsequent to this, five epiphyses, or 

 supplementary centres of ossification, are added. Three of these are small portions of bone, 

 placed on the tips of the spinous and transverse processes : the other two are thin annular 

 plates on the upper and lower surfaces of the body at its circumference. In the lumbar 

 vertebrae two other epiphyses surmount the mamillary processes. These epiphyses appear from 

 the sixteenth to the twentieth year, and are not wholly united to the rest of the vertebra 

 before the twenty-fifth year. The transverse process of the first lumbar vertebra is sometimes 

 developed from a separate centre. The anterior divisions of the cervical transverse processes 

 are for the most part ossified by the extension into them of osseous substance from the 

 neighbouring posterior part of the process and from the arch ; but there are usually separate 

 osseous nuclei for those of the seventh, sometimes also of the sixth, and even the fifth or 

 second vertebras. 



Atlas and axis. The ossification of the atlas and axis differs considerably from that of 



Fig. 20. OSSIFICATION OF THE ATLAS. (E. Quain.) 



A, before birth ; B, in the first year ; 1 & 2, lateral 

 centres of ossification ; 3, ossific centre in the anterior 

 arch. 



the other vertebrae. In the atlas the anterior arch is formed by a strip of cartilage in which 

 ossification, commencing by one or two centres, only appears in the course of the first year 

 after birth. The posterior arch, together with the lateral masses, is formed from two centres 



c 2 



