48 



THE SKELETON 



Lumbar vertebrae. — In the lumbar vertebrae the neuro-central suture is almost transverse, 

 and to the usual number of centres of ossification, two other epiphyses for the mammillary 

 tubercles are added, the centres appearing about puberty. The transverse process of the first 

 lumbar vertebra is occasionally developed from an independent centre. 



The fifth lumbar exhibits in some cases a special mode of ossification in the arch. Instead 

 of two centres, there are four — one on each side for the root, transverse process, and supe- 



FiG. 59. — An Immature Cervical Vertebra. 



Neuro-central suture 



rior articular process, and another on each side for the lamina, inferior articular process, and the 

 lateral half of the spinous process (fig. 60). There may be failure of union of roots with the 

 laminae or of the laminae with one another. 



Sacral vertebrae, — The sacrum ossifies from thirty-five centres, which may be classified as 

 follows: — In each of the five vertebrae there are three primary nuclei — one for the body and two 

 for the arch; in each of the first three the costal element of the lateral mass on each side is 



Fig. 60. — Ossification op the Fifth Lumbar Vertebra. 



Lamina 

 Suture 



Pedicle 



Neuro-central suture 

 Centrum 



formed from a separate nucleus; associated with each body are two epiphysial plates; and on 

 each lateral margin are two irregular epiphyses, one for the auricular surface and another for 

 the rough edge below. 



The centres for the bodies appear about the eighth or ninth week and for the vertebral 

 arches about the sixth month. The arches join the bodies at different times in the different 



Fig. 61. — Sacrum at Bihth to show Centres of Ossification. (Enlarged one-third.) 



Ossific centre in the body of first sacral vertebra. 

 Beneath this are seen in succession the centres in the 

 bodies of the second, third, fourth, and fifth vertebrae 



Ossific centres in the lateral mass' 



vertebrae, ranging from the second year below, to the fifth or sixth year above, and union of the 

 laminae takes place behind some years later, from about the ninth to the fifteenth year. 



The centres for the costal elements :i|)poar outside the anterior sacral foramina, from the 

 fifth to the .seventh month, and ihtjse unite with tlie bodies somewhat later than the arches. 



The centres for the epii)hyHi!il i)latcs appoar about the fifteenth year, and for the auricular 

 epiphyses and the edges below, from the eighteenth to the twentieth year. 



