106 



OSTEOLOGY. 



as fusion between the dens 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 

 fusion of the dens with the body is denned by a small disc of cartilage which persists 

 within the substance of the bone till an advanced period of life. 



A pair of epiphyses placed over the tubercles of the spinous process, if not always 

 present, are at least frequent. 



Sacrum. Each of the sacral segments is ossified from three centres : one for the 

 body, and two for the vertebral arch that for the body, which makes its appearance in the 

 first three sacral vertebrae about the end of the third month, about the fifth to the 

 eighth month for the last two segments. From the two centres for the vertebral arches, 

 which make their appearance about the fifth or sixth month in the higher segments, 

 the laminae, articular processes, and the posterior half of the alee on either side are 

 developed. The sacral 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 

 less extent, in some of the higher segments. The anterior portion of the lateral parts is 

 developed from separate centres which represent the costal elements (Gegenbauer). These 

 appear about the sixth to the eighth month, and may develop in relation to the upper 

 four sacral segments ; more usually they are met with in connexion with 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 parts, 

 which support the hip bones, are formed. The 

 costal elements fuse about the second to the fifth 

 year with the vertebral arches, prior to their 

 union with the bodies ; and the segments of the 

 lateral parts unite with each other sooner than 

 the union of the bodies is effected. The latter 

 only takes place after puberty by the fusion of 

 the epiphysial plates, a pair of which make their 

 appearance between the bodies of each segment. 

 The lower segments begin to unite together about 

 the eighteenth year, but fusion between the first 



and second sacral vertebra is r* ,r? leted ^ 



VERSE EPIPHYSES AT THE EIGHTEENTH the twenty-fifth year or after. In addition to the 

 YEAR. foregoing there are costal and transverse epi- 



physes. According to Fawcett they are arranged 

 as follows. Costal epiphyses : The costal pro- 

 cesses of the I. and II. sacral segments bear at their 



--T.I 



T., Epiphysis of transverse process. 

 C.V., Ventral epiphysis of costal process. 

 C.D., Dorsal epiphysis. 



The numbers indicate the segments to which lateral d inferiorly two such epiphyses, one 

 the epiphyses belong. , J , ,, , J , . . . 



dorsal and one ventral ; these, by their fusion 



and expansion mainly in an upward direction, form a plate the auricular facet. The 

 III. and IV. costal processes have only one epiphysis each, viz., the ventral. All these 

 appear about the eighteenth year. Transverse epiphyses : Epiphyses are developed on all 

 the transverse processes of the sacral vertebrae except the II. Those of the IV. and V. 

 play an important part in the moulding of the lower lateral region of the sacrum. Thus, the 

 transverse epiphysis of the IV. segment becomes comma-shaped by downward and lateral 

 growth, the head of the comma fuses with the costal epiphvsis of the III. sacral segment, 

 which in turn unites with the epiphysis of the transverse process of the V. segment, 

 the ultimate result being a Z-like arrangement on the posterior and inferior aspect of the 

 sacrum. The extremities of the superior spinous processes are occasionally developed from 

 independent epiphyses. On making a median section of an adult bone the persistence of 

 the intervertebral fibro-cartilages between the bodies is indicated by a series of oval cavities. 

 Coccygeal Vertebrae. These are cartilaginous at birth. Each has a separate 

 centre ; the first appears from the first to the fourth year, the second from the sixth to 

 the tenth year, the third and fourth segments at or about puberty. Secondary centres, 

 for the coccygeal cornua and epiphysial plates for the bodies are also described. Fusion 

 of the various segments begins below and proceeds upwards, but is liable to great indi- 

 vidual variation. In advanced life the coccyx is often ossified to the sacrum. 



THE STERNUM. 



The sternum occupies the middle of the upper part of the thoracic wall 

 anteriorly. It is connected on each side with the cartilages of the first seven ribs, 

 and supports, superiorly, the clavicles. It consists of three parts, named respectively 



