SPINE. 



allows them to recover their original dimenfions. See Car- 

 tilage. 



The correfponding faces of the articular procefTes are 

 covered by thin cartilaginous layers, and furuifhed with a 

 ftnall fynovial membrane, which is very clofely drawn be- 

 tween the oppofed furfaces, and contains very little fynovia. 

 Several fliort and irregular, but ftrong ligamentous fibres, lie 

 on this membrane. 



The yellow ligaments (lig. fubflava), fo called from their 

 colour, tie together the laminae of the vertebra;, which do 

 not touch each other, and complete the canal of the fpine, 

 which would be otherwife open at the intervals of their la- 

 mina;. The firft of thefe ligaments is placed between the 

 fecond and third cervical vertebra: ; the lait between the fifth 

 lumbar and the facrum. Each confifts of two portions, a 

 right and left, united at an angle towards the bafis of the 

 fpinous procefs, and having at this union a fmall interval 

 containing a little cellular tifFue. Each portion is attached, 

 above, to the inner furface of the fuperior lamina ; and be- 

 low to the upper edge ot the inferior : hence they are hidden 

 behind, and can only be feen to advantage from the vertebral 

 canal ; they may be beft expofed by fawing out the fpinous 

 procefTes, and their laminae, from the vertebral column, in 

 one continuous piece. They correfpond, in front, to the 

 dura mater, to which they are connefted by a loofe cellular 

 tiliue ; behind, to the inner furface of the upper laminae of 

 each interval, and to the multifidus Ipinse. The angle 

 formed by the union of the two lateral pieces is continuous 

 m the back and loins with the interfpinal ligaments : on the 

 outfide each is contiguous to the fynovial membrane of the 

 articular procefles. Their fibres are numerous and clofely 

 fet ; longer towards the canal, where they appear fmooth 

 and pohflied, than towards the vertebral channel, where they 

 are rough and uneven. There is very little cellular tifl'ue in 

 their compofition, fo that they are diffolved under ebullition 

 with great difficulty, and refill it longer than any analogous 

 organs. They are claltic, very ftrong, fo that vaft force is 

 required to break them : ftronger indeed than the fibro- 

 cartilages, in which the fibres are feparated by much of the 

 pulpy texture. It is very clear that thefe ligaments will 

 powerfully tend to reftore the fpine, after it has been inclined 

 forwards. 



The fpinous procefles, feparated by intervals more or lefs 

 confiderable in different fituations, are united by two kinds 

 of hgaments ; one of which connefts the procefTes them- 

 felves, while the other envelopes their points. 



The interfpmal ligaments (membrana interfpinalis) occupy 

 the intervals of the procefles, but do not exilt in the neck, 

 where the correfponding fpaces are filled by the interfpinales 

 mufcles. Their breadth and ftrength increafe from above 

 downwards ; in the back they are narrow, elongated, and 

 thin, and can fcarcely be faid to exift in the upper part of 

 the region. They are quadrilateral, broader and thicker in 

 the loins, where they may offer confiderable refiftance to the 

 feparation of the procefles. Their points of attachment are 

 the lower edge of one fpinous procefs, and the upper edge 

 of the next : they correfpond, in front, to the angle of union 

 of the two portions of the yellow ligaments ; behind, to the 

 fuprafpinal hgaments ; and on the fides, to the multifidus 

 fpina: and longiffimus dorfi. They are compofed of de- 

 cufTating fibres. 



The fuprafpinal ligament (hg. quo apices vertebrarum 

 conneftuntur) extends along the points of the fpinous pro- 

 cefTes of the back and loins, from the feventh cervical ver- 

 tebra to the fpinous procefles of the facrum. It is very 

 thick in the loins, where it is fo interwoven with the ten- 

 dinous attachments of the mufcles, that they can hardly be 



difl^inguilhed. In the back it is thinner and more diftind 

 from the aponeurofis. The longitudinal direAion of it» 

 fibres ferves to diltinguifh it from the tendons, of wliich the 

 fibres are oblique. Its fibres are of diffL-rent lengths ; the 

 deeped go from bone to bone ; the more fuperficial are 

 longer, palling over one, two, or more vertebrae, and giving 

 origin to the aponeurotic fibres of the neighbouring mufcles. 

 The llvin covers this ligament behind ; adhering to it by a 

 clofe cellular tilfue. 



The ligamentum nuchse, which ariles from the cervical 

 fpinous procefTes, belongs more to the head than to the 

 fpine. It is defcribed under Head. 



The lait vertebra of the loins is articulated to the facrum, 

 jult in the fame way as the individual vertebrae are joined to- 

 gether ; viz. by a fibro-cartilage, by yellow ligaments, by 

 an mterfpinal ligament, and by articular procefTes. 



The Spine conftdered as a Whole. — The twenty-nine bones 

 juft defcribed, ■u/z. the twenty-four vertebra, the facrum, 

 and the four ofla coccygis, are joined by tiie articulations 

 which have been now explained, (all being connefted by the 

 intervention of fibro-cartilages, except the atlas,) fo as to 

 form, by their afTemblage, the itrong but flexible bony 

 column which fuftaiNs the head, forms the bafis of the 

 trunk, affords a point of attachment to the upper limbs, 

 and below is received between and fupported by the haunch 

 bones. We diftinguilh in it an anterior, a pollerior, and 

 two lateral regions, and two extremities. We may obferve, 

 in general, that the whole column increafes in fize from 

 above downwards, as it has to fupport an increafing weight ; 

 but to this there are fome exceptions, that will be noticed. 



The anterior region, compofed of the bodies of the ver- 

 tebrae and the intermediate fibro-cartilages, prefents in fome 

 degree the appearance of a bony pillar, which term is httle 

 applicable to the rows of bony procefTes, which form the 

 lateral and pofterior afpefts of the fpine. This region is 

 broad in the neck, narrow in the back, and again fpreads 

 out in the loins. Its breadth in the firft fituation arifes from 

 the fmallnefs and inconfiderable prominence of the vertebral 

 bodies ; in confequence of which the tranfverfc procefTes in 

 this region form part of the anterior afpeft of the fpine ; 

 while in the back and loins, the bodies form, by their bold 

 convex projeftion, the whole front of the column. The 

 front of the fpine prefents a feries of fuperficial tranfverfc 

 excavations, and of prominent edges which bound them : 

 the number of the latter is double that of the former, as 

 each tranfverfc channel is bounded above and below by a. 

 ridge. Thefe excavations are confined to the front in the 

 neck ; but they reach to the fides in the middle of the 

 column. The anterior vertebral ligament, the refti capitis 

 majores, the longi colli, the vena azygos, thoracic duft, 

 aorta, and inferior vena cava, cover the fpine in front. 



We obferve, on the pofterior afpeft, in the middle hnc, 

 the feries of fpinous procelTes, projcfting horizontally at 

 the upper and lower parts, and very flanting in the middle. 

 They are feparated by intervals, whicli arc large in the neck 

 and ttill more fo in the loins ; but very much narrowed in 

 the back, in the middle of which the procefles aflually 

 overlap. In the neck and loins there are openings between 

 the laminx, leading into the vertebral canal, in the flu-le- 

 ton ; but the flanting of the fpinous procefles covers thefe 

 in the back. Tlie points of the fpinous procefTes are gene- 

 rally all in the fame line ; but there may be deviations, arif- 

 ing either from a lateral inclination of the procefs, or from 

 an unnatural pofition of the vertebra. On each fido of the 

 fpinous procefles there is a longitudinal hollow, beginning 

 at the upper extremity of the column, and ending below 

 upon the facrum. Thefe lateral hollows arc broad above, 

 3 Z 2 contraftcd 



