415 



processes, and the posterior half of the alae on either side are de- 

 veloped. The spinal canal is not enclosed till the seventh to the tenth 

 year, the laminae usually failing to meet in the lowest segment, and 

 occasionally, to a greater or a less extent, in some of the higher seg- 

 ments. The anterior part of the lateral masses is developed from se- 

 parate centres which represent the costal elements (Gegenbaur). 

 These appear about the sixth to the eighth month, and may develope 

 in relation to the upper four sacral elements, more usually they are 

 met with in the first three, and exceptionally they may be found only 

 in the upper two. It is by fusion of these with the posterior arches 

 that the lateral masses which support the innominate bones are formed. 



The costal elements fuse about the second to the fifth year with 

 the neural arches, prior to their union with the centra, and the seg- 

 ments of the lateral masses unite with each other sooner than the 

 union of the bodies is eff'ected. The latter only takes place after puberty 

 by the fusion of the epiphyseal plates a pair of which make their 

 appearance between the centra of each segment. The lower segments 

 begin to unite together about the eighteenth year, but fusion occurs 

 between the first and second sacral vertebrae, is not completed till the 

 twenty -fifth year or after. In addition to the foregoing, two thin 

 osseous laminae are developed in the cartilage covering the outer sur- 

 face of the alar mass. The upper of these overspreads the auricular 

 surface whilst the lower forms the sharp edge below. The extremities 

 of the upper spinous processes are occasionally developed from inde- 

 pendent epiphyses. On making a mesial section of an adult bone the 

 persistence of the intervertebral discs between the centra is indicated 

 by a series of oval cavities. 



Tablified these centres may be expressed thus: 



Other text-books vary in minor respects from the statements given 

 above. 



So far as they go, speaking generally, the various descriptions may 

 be taken as accurate, but in detail it is doubtful if the generally ac- 

 cepted description of the ossification of the auricular surfaces and the 

 tuberosities is quite right. No mention is made of the fact that the 



