

THE SACRAL AND COCCYGEAL VERTEBRA 



113 





About the sixteenth year (Fig. 102), five secondary centers appear, one for the tip of each transverse 

 process, one for the extremity of the spinous process, one for the upper and one for the lower 

 surface of the body (Fig. 103). These fuse with the rest of the bone about the age of twenty-five. 



Exceptions to this mode of development occur in the first, second, and seventh cervical verte- 

 brae, and in the lumbar vertebra?. 



Atlas. The atlas is usually ossified from three centers (Fig. 104). Of these, one appears in 

 each lateral mass about the seventh week of fetal life, and extends backward; at birth, these 

 portions of bone are separated from one another behind by a narrow interval filled with cartilage. 

 Between the third and fourth years they unite either directly or through the medium of a separate 

 center developed in the cartilage. At birth, the anterior arch consists of cartilage; in this a 

 separate center appears about the end of the first year after birth, and joins the lateral masses 

 from the sixth to the eighth year the lines of union extending across the anterior portions of 

 the superior articular facets. Occasionally there is no separate center, the anterior arch being 

 formed by the forward extension and ultimate junction of the two lateral masses; sometimes 

 this arch is ossified from two centers, one on either side of the middle line. 



Epistropheus or Axis. The axis is ossified from five primary and two secondary centers (Fig. 

 105). The body and vertebral arch are ossified in the same manner as the corresponding parts 

 in the other vertebrae, viz., one center for the body, and two for the vertebral arch. The centers 

 for the arch appear about the seventh or eighth week of fetal life, that for the body about the 

 fc arth or fifth month. The dens or odontoid process consists originally of a continuation upward 

 of the cartilaginous mass, in which the lower part of the body is formed. About the sixth month 

 of fetal life, two centers make their appearance in the base of this process: they are placed 

 laterally, and join before birth to form a conical bilobed mass deeply cleft above; the interval 

 between the sides of the cleft and the summit of the process is formed by a wedge-shaped piece 

 of cartilage. The base of the process is separated from the body by a cartilaginous disk, which 

 gradually becomes ossified at its circumference, but remains cartilaginous in its center until 

 advanced age. In this cartilage, rudiments of the lower epiphysial lamella of the atlas and 

 the upper epiphysial lamella of the axis may sometimes be found. The apex of the odontoid 

 process has a separate center which appears in the second and joins about the twelfth year; this 

 is the upper epiphysial lamella of the atlas. In addition to these there is a secondary center for 

 a thin epiphysial plate on the under surface of the body of the bone. 



The Seventh Cervical Vertebra. The anterior or costal part of the transverse process of this 

 vertebra is sometimes ossified from a separate center which appears about the sixth month of 

 fetal life, and joins the body and posterior part of the transverse process between the fifth and 

 sixth years. Occasionally the costal part persists as a separate piece, and, becoming lengthened 

 lateralward and forward, constitutes what is known as a cervical rib. Separate ossific centers 

 have also been found in the costal processes of the fourth, fifth, and sixth cervical vertebrae. 



Lumbar Vertebrae. The lumbar vertebrae (Fig. 106) have each two additional centers, for 

 the mammillary processes. The transverse process of the first lumbar is sometimes developed as 

 a separate piece, which may remain permanently ununited with the rest of the bone, thus form- 

 ing a lumbar rib a peculiarity, however, 



Center for 

 neural arch. 



Center for 

 neural arch. 





Costal 

 element' 



rarely met with 1 . 



Sacrum (Figs. 107 to 110). The body 

 of each sacral vertebra is ossified from a 

 primary center and two epiphysial plates, 

 one for its upper and another for its under 

 surface, while each vertebral arch is ossi- 

 fied from two centers. 



The anterior portions of the lateral parts 

 have six additional centers, two for each 

 of the first three vertebra?; these represent 

 the costal elements, and make their ap- 

 pearance above and lateral to the anterior 

 f sacral foramina (Figs. 107, 108). 

 On each lateral surf ace two epiphysial plates are developed (Figs. 109, 110) : one for the auric- 

 ular surface, and another for the remaining part of the thin lateral edge of the bone. 1 



PERIODS OF OSSIFICATION. About the eighth or ninth week of fetal life, ossification of the 

 central part of the body of the first sacral vertebra commences, and is rapidly followed by deposit 

 of ossific matter in the second and third; ossification does not commence in the bodies of the 

 lower two segments until between the fifth and eighth months of fetal life. Between the sixth 



Center for 

 body. 



Lateral 

 epiphysis. 



Fia. 110. Base of young sacrum. 



Lateral 

 epiphysis. 



1 The ends of the spinous processes of the upper three sacral vertebrae are sometimes developed from separate 

 epiphyses, and Fawcett (Anatomischer Anzeiger, 1907, Band xxx) states that a number of epiphysial nodules may be 

 seen in the sacrum at the age of eighteen years. These are distributed as follows: One for each of the mammillary pro- 

 cesses of the first sacral vertebra ; twelve six on either side in connection with the costal elements (two each for the first 

 and second and one each for the third and fourth) and eight for the transverse processes four on either side one each 

 for the first, third, fourth, and fifth. He is further of opinion that the lower part of each lateral surface of the sacrum 

 is formed by the extension and union of the third and fourth "costal" and fourth and fifth "transverse" epiphyses. 





