22 VERTEBRAL COLUMX. 



each vertebra, epiphysial plates are formed after puberty, as in other vertebrce, 

 and two flat iiTegxdar plates of bone are added to each lateral surface of the 

 sacrum, the uppeimost of which extends over the sides of the fii'st two or three, 

 while the lower connects the remaining two. These appear from the 1 8th to the 

 20th year, and are imited about the 25th. The bodies of the sacral vertebra3 are at 

 first separated by intervertebral plates, but about the ISth year, in the case of 

 tlie lower vertebraj, ossification begins to extend through these plates and the 

 epiphyses, so as completely to luiite the adjacent bodies. The ossific union 

 of the first and second bodies does not take place tUl the 2r)th year or later 

 Previous to this, the lateral masses have coalesced nearly in the same order as 

 the bodies. 



The deficiency of the spine and dorsal part of the lamhiaj usi^ally existing in 

 the fifth sacral vertebra, and not unfrequently extending to the fourth, but more 

 rarely to the third, may be attributed in part to the non-extension of ossification 

 in that du-ection : but such varieties of form, like many others to which the 

 sacral vertebrte are subject, are probaV)ly intimately connected with the nature 

 and development of the formative matrix of the bones. The more completely 

 open state of the sacral canal posteriorly found in cases of spina-biflda is un- 

 doubtedly connected with early morbid changes interfering with the natural 

 process of development. 



Coccyg-eal Vertebrae. — Each of the coccygeal vcrtebrte is ossified from a, 

 distinct piece of cartilage, and usually from a single centre, but in the up])er 

 sometimes from two centres. Ossification commences in the first generally about 

 the time of buth ; in the second, from the 5th to the lUth year ; in the third, 

 some time before, and in the fourth, some time after puberty. The ossific union 

 of the three lower coccygeal vei-tebra; occui's before middle life : their union with 

 the first, and the union of this with the sacrum, belong to the later periods of life. 



GENERAL AND SERIAL HOMOLOGY OF THE VERTEERiE. 



The study of the various forms presented by the parts of the vertebral column, 

 and of its relation to the rest of the skeleton in man and animals, as also 

 of its development in the foetus, has led to the foiTuation of the general 

 views of homology refeiTcd to in the introduction. These views originated, in 

 somewhat different fomas, mainly with Oken, Carus, Geoffrey St. Hilaii-e, and 

 Owen ; and, with various modifications and extensions by more recent writers, 

 as Goodsir, Huxley, Gegenbam-, St. George Mivart, and Flower, are now admitted 

 by almost all anatomists, in some shape or other, as the basis of a morphological 



Fig. 21. — Views op the Different Vertebrae froji above to illvstrate their 

 Homologies. (A. T. ) 

 1, atlas; 2, axis; 3, si.xth cervical; 4, seventh cervical with supernumerary rilis ; 

 5, middle dorsal ; 6, upper dorsal, with costal arch and sternum attached ; 7, middle 

 lumbar; 8, first lumbar with supernumerary ribs ; 9, lower lumbar ; 10, upper sacral ; 11, 

 upper sacral vertebra, presenting the lumbar form on the right side, as in the oblique 

 pelvis ; 12, fourth sacral vertebra in a young subject ; 13, four coccygeal vertebra?. 

 In the several figiu-es the parts are indicated by letters as follows, viz., in 1, s, spine ; 

 n, neural arch ; c', the space occupied by the processus dentatus, or displaced body ; 

 fi, anterior or precentral arch ; ar, superior articular process : in 2, c", processus dentatus ; 

 ar, superior articular process ; z' inferior articular process : in 3, f, centrum or body ; 

 r, z', superior and inferior articular processes : in 4, t, t, transverse processes ; r, v, ver- 

 tebrarterial foramina ; co, moveable right supernumerarj- or cervical rib ; x, with a dotted 

 line marks the place where an anchylosed rib on the left side may be considered to be 

 superadded to the transverse process (diapophysis and jiarapophysis) of the vertebra : in 5, 

 t, transvei-se process with costo-transverse facet ; cc, costo -central facet : in 6, r, ver- 

 tebrarterial interval ; ct, costo-transverse, and cc, costo-central articulations ; co, first 

 rib : in 7, m, mammillary, and a, accessory tubercles ; t, transverse process : in 8, co, 

 co', left and right supernumerary ribs : in 10, I, the lateral mass : in 11, V, place of the 

 lateral mass, remaining undeveloped in this instance : in 12, tl, the transverse process 

 and lateral mass which unite with the corresponding parts above ; /, /', anterior and 

 jiosterior sacral for.tmina thus formed : in 13, c, the centrum or body, which alone reiaains 

 in the last coccygeal vertebra. 



