SPINE. 



much ftrength, as if it were compofed of a fmgle piece, al- 

 though a power of motion is combined with that capacity 

 for refiftance. The numerous joints, and the great quantity 

 of foft elaRic matter in the fpine, give a fpring to all the 

 motions of the trunk, and (top the effeft of all (hocks, fo 

 as to prevent their propagation, and to obviate conculTion 

 of important organs, particularly of the brain. But, be- 

 fides the articulations which join the component pieces of 

 the fpine, there are feveral others, by which various parts 

 are joined to the fpine. Such are the joints of the head 

 with the firft and fecond vertebrae of the neck, and of thefe 

 vertebra with each other : thefe, and the motions they exe- 

 cutt, are coniidered under the article Head. The con- 

 nection of the ribs with the dorfal vertebra; is defcribed 

 under Lungs. The articulation of the facrum with the 

 oflfa innorainata, and with the coccyx, and of the diflFerent 

 pieces of the coccyx with each other, are defcribed under 

 Pelvis. 



Articulations of the Vertehm. — Thefe bones are joined, 

 lit, by their bodies ; 2dly, by their articular proceffes ; 

 3dly, by their laminx; ; and 4thly, by the fpinous procelFes. 

 The mode of connection is the fame throughout the fpine, 

 excepting in the cafe of the atlas and the axis. Of the 

 uniting media, however, fome form feparate and infulated 

 organs at each intervertebral interval ; fuch are the fibro- 

 cartilages, and the yellow ligaments : others conititute 

 common organs, embracing at the fame time the whole 

 vertebral column, or its greatelt part, as the anterior and 

 po(terior vertebral and the fuprafpinal ligaments. Yet 

 the fibres of the latter do not run through the whole 

 length. 



I'he bodies of the vertebrx are united by an anterior and 

 a polterior vertebral ligament, and by a fibro-cartilage be- 

 tween every two bones. 



The anterior vertebral ligament, or fafcia longitudinalis an- 

 terior, occupies the anterior furface of the column, extending 

 from the axis to the upper part of the facrum. It is not 

 equally ftrong nor broad throughout : it is narrow in the 

 neck, broader in the back, and (till wider in the loins. In 

 the firft fituation it is thin, ftronger in the fecond, and again 

 rather thin in the loins, where the tendons of the crura dia- 

 phragmatis are intermixed with it. The (ibres of this liga- 

 ment do not run through the whole length of the column ; 

 fome end and others begin in each bone. This ligament con- 

 filts of a thin llratum clofely adhering to the bone, and co- 

 vered, in the neck, by the pharynx and oefophagus, in the 

 back, by the latter, by the aorta, vena azygos, and thoracic 

 duft, and in the loins by the aorta and the inferior vena cava. 

 At the fides it correfponds, in the neck, to the refti majores 

 antici and longi colli ; in the loins to the pfoae. It adheres to 

 the fibro-cartilages, and to the projefting edges of the ver- 

 tebral bodies, more clofely than to the concavities of the 

 latter. The more fuper(icial (ibres go from one vertebral 

 body or fibro-cartilage to the fourth or fifth below ; others 

 belong to three bones or fibro-cartilages ; and the deepe(t 

 only to two. The fibres are interwoven with thofe on the 

 froHt of the fibro-cartilages ; and they leave fmall intervals 

 for the palTage of velTels. At the fides of this ligament in 

 the neck, under the longi colli, are two fmall fibrous fafci- 

 culi for each vertebra, palling obliquely downwards and 

 outwards from the vertebra above to that next below it. 



The pofteriur ligament (fafcia longitudinalis poftica) oc- 

 cupies the pofterior afpeft of the vertebral bodies, where 

 they form the front of the canal, extending from the axis and 

 the occipitoaxoid ligament, or apparatus colli hgamentolus, 

 to the facrum. It is more denfe in its ftrufture than the 

 anterior, and appears more diftina, fmooth, and ihining. 



The narrowed part of it is in the back : it enlarges at the 

 fibro-cartilages, and is contracted at the bodies of the ver- 

 tebra; ; thus, when viewed in its whole length, it is alter- 

 nately contrafted afid expanded at each vertebra and its 

 neighbouring cartilage. The dura raater covers it behind, 

 feparated from it by a loofe cellular tiffue, never contain- 

 ing fat, but often much ferous fluid. It correfponds ia 

 front to the fibro-cartilages and the bodies of the vertebrz, 

 adhering lefs clofely to the latter than to the former. Like 

 the anterior ligament, it confifts of fuperficial and deep- 

 feated fibres, of which the former are the longed, and pafs 

 over three or four vertebrae, while the latter go from one 

 bone or fibro-cartilage to the next. 



The fibro-cartilages (hgaraenta intervertebralia) are or- 

 gans, of which the nature is little underllood, holding the 

 middle place, in point of ilrudture, between ligament asd 

 cartilage, and occupying the intervals of the vertebral bodies 

 throughout the column, excepting between the atlas and 

 axis. Their form varies according to that of the bodieg 

 which they unite ; and confequently is different in the neck, 

 back, and loins. Their thicknefs increafes fucceflively from 

 above downwards ; fo that the lumbar are feparated by 

 larger intervals than the cervical and dorfal vertebrx. More- 

 over, they are thicker in front than behind, in the neck : on 

 the contrary, they are thickell behind in the back ; and the 

 arrangement in the loins is the fame as in the neck : thefe 

 differences are obvioufly connefted with the natural bend- 

 ings of the column. The fibro-cartilages adhere very in- 

 timately above and below to the correfponding flat furfaces 

 of the vertebra:. In the foetus they adhere to the cartilages 

 of oflification ; when they are removed nothing remains at- 

 tached to the vertebra: ; but, in the adult, the bony fibres 

 and thofe of the fibro-cartilages are fo completely identified, 

 that we find no inftances in the animal economy of itronger 

 union. The circumference of thefe fubftances correfponds 

 to the anterior and polterior vertebral ligaments : on each 

 fide, they form part of the holes through which the fpinal 

 nerves pafs ; and in the back they contribute to the arti- 

 cular cavities for the heads of the ribs. 



The fibro-cartilages are formed externally of concentric 

 fibrous laminK, numerous in front and at the fides, fewer 

 behind, with decuffating fibres, feparated by more confider- 

 able intervals as we approach the centre. In the latter we 

 find a foft pulpy tilTue, increafing in quantity as the inter- 

 vals increafe in breadth. The fibrous laminae degenerate 

 gradually into the pulpy ftruiture, which occupies alone the 

 middle of each fibro-cartilage. This tiflue is moft abundant 

 in the child, where it is alfo foft, whitifh, and even nearly 

 tranfparent, while it is yellowilh and thick in the adult. It 

 becomes denfc and compaA in the old fubjeft, and is con- 

 Itantly diminilhing. To it the fibro-cartilages owe their 

 pliancy and elallicity ; while their Itrength refides in the 

 laminx, which inclofe this foft (Irudture. Hence the fpine 

 is diftinguifhed by the firft property in infancy ; while the 

 other predominates afterwards. The laminx foon become 

 red when immerfed in water : the middle part fwells and rifes 

 jnto a conical projection. If the fpine be fawn through 

 longitudinally, the fibro-cartilage fwells out, on the cut fur- ' 

 face, beyond the bone. The effect of thefe fubftances in 

 reftoring the column, when it has been bent in any diredtion, 

 is very obvious. The inflexion compreffes the fibro-cartilages 

 at the bent part ; and they reftore themfelves as foon as the 

 comprcffing caufe ceafes to aft. When the body has been 

 long ereft, the fibro-cartilages yield to the weight which 

 pre(res them from above, and thus the length of the fpine, 

 and confequently of the body, is diminilhed: the ceflation of 

 this preflure, when the body is in the horizontal pofition, 



allows 





