DEVELOPMENT OF THE VERTEBRA. 



129 



lumbar region. The tips of the spinous and transverse processes develop from cen- 

 tres which appear about puberty and fuse about the eighteenth year. A thin epi- 

 physeal disk, covering the upper and lower surfaces of each body, grows from a centre 

 seen about the seventeenth year, and joins by the twentieth, the line of union per- 

 sisting a year or two longer. The mammillary processes of the lumbar region arise 

 from separate centres ; so do also the costal elements of the sixth and seventh cer- 

 vicals, and sometimes that of the first lumbar. In cases in which this costal element 

 of the seventh cervical remains free there is a cervical rib and no transverse fora- 

 men ; exceptionally in these cases a foramen persists. According to Leboucq,^ the 

 development of the anterior limb of the transverse process of the cervical vertebrae 

 is more complicated than is usually taught. There is a slight outward projection 

 from the ventral side of the body rep- 



FiG. 157. 



resenting the prominence for the head 

 of the rib to rest upon ; this grows out- 

 ward and meets a growth from the 

 transverse process that grows inward 

 like a hook. This inward growth rep- 

 resents what we commonly call the 

 costal element of a cervical vertebra, 

 but there may be also a separate ossi- 

 fication representing an actual rib, — 

 namely, a small piece of bone on the 

 ventral aspect of the tip of the trans- 

 verse process of the seventh cervical 

 vertebra. When a separate ossifica- 

 tion occurs in this region in the fifth 

 or sixth vertebra, it is situated still 

 more externally than in the seventh, 

 and forms the floor of the gutter be- 

 tween the anterior and the posterior 

 tubercles, which is the true costal ele- 

 ment. It is probable that in certain 

 cases of cervical ribs accompanied by 

 a transverse foramen, the latter is en- 

 closed by the hook-like process from 

 the transverse process meeting the 

 growth from the body of the vertebra, 

 and that the rib coming from the 

 separate ossification lies anteriorly to 

 it and distinct from it. At birth the 

 lumbar articular .processes resemble 

 the thoracic. The type changes in 

 early childhood. 



The Sacrum. — Each sacral ver- 

 tebra has the three primary centres of 

 the others, the median ones appearing before the lateral of the same vertebra. Proba- 

 bly the median centres of the first three appear first and then the lateral ones of the 

 first vertebra ; data, however, are wanting for a definite statement. The time of the 

 first appearance of ossification in the sacral vertebrae is very variable ; probably the 

 earliest median centres appear about the beginning of the fourth month and the 

 lateral ones some weeks later. In a skiagraph of a foetus estimated to be about 

 three and a half months old the median centres of the upper three vertebrae and 

 the lateral ones of the first are visible. This is, perhaps, earlier than the rule. Little 

 progress in ossification of the last two sacrals takes place before birth. The lateral 

 centres join the median, in the lower vertebrae, during the second year ; in the upper 

 ones, three or four years later. In the upper three vertebrae a centre appears out- 

 side the anterior sacral foramen, from which a part of the lateral mass is developed. 



' M^moires couronn^s, etc., Acad. Royale des Sciences de Belgique, tome Iv., 1896. 



9 



Ossification of the vertebrae. A, cervical vertebra at 

 birth ; centres for body (a), neural arches (d), and costal ele- 

 ment (c). B, dorsal vertebra at two years; cartilaginous 

 tips of transverse (a) and spinous {b) processes; d, centre 

 for body. C, lumbar vertebra at two years ; position of ad- 

 ditional later centres for various processes indicated (a, d, c) ; 

 d, centre for body. 



