OSSIFICATION OF THE VERTEBRA. 89 
of the superior articular processes, and extend backwards into the lamineze, outwards into 
the transverse processes, and forwards into the pedicles. These latter project anteriorly, 
and form a considerable portion of the postero-lateral aspects of the body, from which, 
however, they are separated by a cartilaginous strip—the neuro-central synchondrosis— 
which does not entirely disappear until about the fifth or sixth year. It is important to 
note that in the thoracic region the costal facets lie behind the neuro-central synchondrosis, 
and are therefore borne on the lateral aspects of the pedicles. Fusion of the laminze in the 
mesial plane behind begins, after birth, in the lumbar region and extends upwards, so 
that by the fifteenth month or thereabouts the arches in the cervical region are com- 
pleted behind. In the sacral region ossification is slower, the spinal canal not being 
enclosed till the seventh to the tenth year. The spinous processes are cartilaginous at 
birth, but these become ossified by the extension into them of the bony laminee. 
At puberty certain secondary centres or epiphyses make their appearance ; these are 
five in number. One caps the summit of the spinous process, except in the cervical 
region. <A single epiphysis on either side appears at the extremity of the transverse 
process, and in “the thoracic region assists in forming the articular surface for the tubercle 
of the rib. Two epiphysial plates are formed—one for the upper, and the second for the 
lower surface of the body, including also that part which lies behind the neuro-central 
synchondrosis and for med by the pedicle ; ; from these the thickened circumference of both 
upper and lower aspects of the body are derived. Fusion of these centres with the rest 
of the bone is not complete till the twenty-fifth year. 
In the cervical region independent centres are described as occurring in the anterior 
roots of the transverse processes of the sixth and seventh vertebree. These correspond to 
the costal element, and may occasionally persist in the form of cervical ribs. Elsewhere 
they are formed by lateral extensions from the pedicle. 
In the lumbar region the transverse process of the first lumbar vertebra is occasionally 
associated with an independent costal centre, which may blend with it, or persist as a 
lumbar rib. The mammillary processes are derived from separate epiphyses. The neural 
arch of the fifth lumbar vertebra is occasionally developed from two centres on either side, 
as is demonstrated by the fact that the arch is sometimes divided by a synchondrodial 
joint running obliquely across between the superior and inferior articular processes on 
either side. (See ante, p. 81; also Vortschritte auf dem Gebiete der Réintgenstrahlen. 
Erganzungsheft i. ; “die Entwickelung des menschlichen Knochengeriistes wahrend des 
fotalen Lebens,” von Lambertz. ) 
Atlas.—The lateral masses and posterior arch are developed from two centres—one on 
either side—which correspond with the centres from which the neural arches of the other 
members of the series are developed. These make their appearance about the seventh 
week, and do not unite posteriorly till after the third year. Their point of union is 
sometimes preceded by the formation of a distinct spinal nucleus (Quain). The anterior 
arch is developed from centres variously described as single or double, which appear in 
one of the hypochordal arches of cartilage described by Froriep (Arch. f. Anat. u. 
Physiol., Anat. Abth. 1886) which here persists. In this cartilage, ossification commences 
during the first year of life. Union with the lateral masses is delayed till six or eight 
years after birth. The external extremities of the anterior arch assist in forming the fore 
part of the superior articular processes. 
The Axis ossifies from five primitive centres. Of these, two—one on either side— 
appear about the seventh week, and form the articular and transverse processes, together 
with the laminze and spine. One, or it may be two, nuclei appear in the lower part of the 
body about the fifth month. The upper part of the body, including a small part of the 
superior articular process, and the base of the odontoid process, are developed from two 
laterally-placed nuclei which appear shortly after, and fuse together at the seventh or 
eighth month, so that at birth the bone consists of four pieces. Fusion between these 
parts takes place in the following order :—The odontoid unites with the body and lateral ° 
parts about the third or fourth year; union between the two lateral portions posteriorly 
and the body and lateral parts in front, is complete at from four to six years. 
The summit of the odontoid process is developed from a separate centre, occasionally 
double, which appears from the third to the fifth year, and fuses with the rest of the bone 
from the eighth to the twelfth year. About puberty an annular epiphysis is developed on 
the under surface of the body, with which it is completely united during the twentieth to 
the twenty-fifth year. Some authorities state that a few granules between the base of the 
odontoid and the upper surface of the body represent the superior epiphysial plate ; but 
as fusion between the odontoid and the body occurs before the time for the appearance of 
these secondary epiphysial plates, this can hardly be regarded as correct. The line of 
