SPINE. 



from the tenth to the twelfth ; and the two laft have no fur- 

 face for articulation with the ribs. 



The configuration of the twelfth dorfal vertebra differs 

 very little from that of the lumbar. 



To the vertebfE of this region the following mufcles are 

 affixed : viz. fplenius capitis and colli, trachelomaftoideus, 

 biventer cervicis, complexus, longus colli, tranfverlalis 

 colli, femifpinalis colli, femifpinalis dorfi, multifidus fpins, 

 facrolumbalis, levatorcs coitarum, intertranfverfales and in- 

 terfpinales dorfi, latiffimus dorfi, rhomboideus major, tra- 

 pezius, ferratus pofticus fupcrior and inferior. 



The liimbiir ■vcrlnbris are (eldom fix in number, and more 

 rarely four. Their great fize, which increafcs down to the 

 lafl, diltinguifhes them from thofe of the back and neck ; 

 while the thick fibro-cartilages, by which they are joined 

 together, and the free fpace between their fpinous procefles, 

 give them confiderable power of motion. The bodies are 

 large and cyhndrical, with flat furfaces above and below, 

 excepting the inferior, which is cut off obliquely, to ac- 

 commodate it to the facruni, with which it is united to form 

 the promontory : the ring is triangular, and larger than m 

 the neck. The lamina: are thick and Itrong, and form a 

 large fpinous procefs, which is flattened laterally, termi- 

 nating above and below in a thin edge, and forming a 

 rounded end behind. That of the laft is very fhort, and 

 fometimes entirely wanting. The tra:.fverfe procelTes are 

 flattened, and rather turned backwards: it is fhort in the 

 firft, increafes in the fecond and third, then again diminifhes. 

 The articular procefles are perpendicular ; the fuperior 

 flightly concave, and the inferior proportionally convex. 

 The former have their articular faces turned inwards and 

 backwards ; the latter outwards and forwards : the fpace 

 between the fuperior is, therefore, neceiTanly more con- 

 fiderable than that between the inferior. 



The following are the mufcles attached to the lumbar 

 vertebrae ; wz. interfpinales and intertranfverfales lum- 

 borum, fpinalis dorfi, multifidus fpins, quadratus lumborum, 

 obliquus internus and tranfverfus abdominis, facrolumbalis 

 and longifTimus dorfi, ferratus pollicus inferior, the dia- 

 phragm, the pfoa; major and minor. 



The bodies of the vertebrte confill almoft entirely of 

 fpongy texture ; it is covered by a very thin layer of com- 

 paft bone : hence a vertebra, when thoroughly cleaned, is 

 very light in comparifon to its bulk. In the recent ftate it 

 appears bloody and medullary. The circumference of the 

 two furfaces is fmooth, the centre rougher. At the fame 

 time that the cellular itrufture of the vertebral bodies in- 

 creafes the ftrength of the column, without adding to its 

 weight, it makes thefe bones liable to thofe affeftions which 

 belong more particularly to fuch ftrufture. The compaft 

 tiifuc is tolerably abundant in the atlas and axis ; and it pre- 

 dominates confiderably in the procefles, which, however, 

 are cellular in their middle, and in parts where they are 

 fwelled, as at the ends of the fpinous procefles in the loins, 

 &c. The offification of the vertebrx goes on in three pieces ; 

 one for the body, and the two others for the lateral and 

 poftcrior parts : yet feparate points may be fometimes feen 

 at the bafes of the fpinous procefles. The lateral portions 

 are united to each other behind, at the bafis of the fpinous 

 procefs ; and they are united in front to the body, at the 

 fituation of the articular procefles. The atlas ufually has 

 five primitive bony pieces; one for the anterior arch, tv,-o 

 for the pofterior, and one for each fide. 



We have included the facrum and the os coccygis in the 

 enumeration of pieces compofing the fpine, although they 

 are generally denominated bones of the pelvis. Their de- 

 fcription may in truth be eonneded, without impropriety, 



either with that of the laft mentioned cavity, or of the ver- 

 tebral column. They belong, however, more naturally to 

 the latter. The facrum is formed on the fame model as the 

 vertebrae, and confifts originally of five dillinft pieces, jult 

 like vertebrae, united by fibro-cartilages ; differing from 

 vertebrae only in fome infignificant points of fize, figure, 

 &c. Thefe pieces are indeed foon confolidated into one 

 bone, which then has much lefs refemblance to the vertebrae 

 than it had before. One great office of the fpinal column, 

 that of continuing and protefting the medulla fpinahs, be- 

 longs equally to the facrum. The modification which the 

 fpine exhibits in this part, arifes from the attachment of the 

 lower limbs : a large furface is neceffary for this purpofe, 

 and a ftrong bone ; and thefe conditions are anfwered in the 

 facrum, w!iich in every other refpeft has the configuration 

 belonging to the fpine. 



The facrum (os latum, clunium'' is the largeft bony piece 

 of the vertrbul column, placed immediately below the lait 

 lumbar vertebra, and at the back of the pelvis ; fupporting, 

 above, the lead, upper limbs, fpine, and fuperior part of 

 the tru' k, and traiifmitting the weight thus received from 

 the laft umbar vertebra to the pelvis, where its broad fides 

 are Itrongly tied to the ofTa innominata, between which it is 

 received like a wedge; and containing the lower extremity 

 of the medulla fpinalis. Its bafis is joined to the laft lumbar 

 vertebra, in the fame way as the individual vertebrx are 

 connedled to each other ; its apex is united to the firft bone 

 of the coccyx. When viewed in its fituation, it is not 

 placed perpendicularly, but turned backwards, making an 

 angle with the lunbar vertebrae, called the promontory. 



The figure of the bone is wedge-fliaped or triangular, 

 with the bafis turned upwards, the apex downwards, and the 

 two fides placed laterally. It is fymmetrical. It is not only 

 broadefl above, but alfo thickeft from before backwards, 

 and gradually diminifhes downwards in both thefe directions. 

 It is concave in front, and tolerably fmooth, convex, and 

 rugged behind. We fhall defcribe its fpinal, pelvic, ver- 

 tebral, and coccygeal furfaces, and the two lateral fides. 



The fpinal furface is convex, very irregular, and covered 

 by the origins of the mufcles, which fill the lateral hollows 

 of the fpinal column. We obferve in it, ill, on the middle 

 line, four eminences, diminifhing in fize from above down- 

 wards, analogous to the fpinous procefles of the vertebrx, 

 of vi'hich they continue the feries, fometimes running into a 

 continuous bony ridge. Thefe are jhe fpinous procefles of 

 the facrum, affording points of attachment to mufcles. 

 They are terminated below by a triangular opening, the end 

 of the facral canal, which is clofed by the pofterior facro- 

 coccygeal hgament, and bounded laterally by two prominent 

 knobs, which are ufually articulated to two correfponding 

 ones of the coccyx. Under thefe, fometimes called the 

 defcending procefles of the facrum, the lalt facral nerve 

 pafles. The inferior opening of the facral canal is fome- 

 times much more extenfive, reaching nearly to the upper 

 part of the bone, fo that the canal is flit in its whole length : 

 the opening in fuch inftances is ttill occupied by ligament. 

 2dly. On each fide, a rough deprelTion above, for the in- 

 fertion of powerful ligaments, which tie the facrum to the 

 OS innominatum ; and, lower, four pofterior facral foramina, 

 fituated in a channel continuous with that of the vertebn, 

 but fhallower, and filled by the lumbar mufcles. Thefe 

 holes, diminifhing in diameter from above downwards, are 

 traverfed by the pofterior branches of the facral nerves, and 

 communicate with the canal of the bone : they are bounded 

 externally by more or lefs diltinft prominences, which may 

 be confidered as reprefenting the tranfverfe procefTes of the 

 vertebrae. 



The 



