SPINE. 



pofition, but the diverfities of their external forms charac- 

 terize them. We (hall firft defcribe the general form, and 

 then notice the particular modifications of the vertebrse. 



Geiifral Form of the Fertebra.— They confia of various 

 irregular and prominent portions, feparated by different in- 

 tervals, and united by different plates. The principal part 

 of the bone in fize is the anterior prominence, called the 

 body ; it is cylindrical or oval, and reprefents the feftion of 

 a cylinder, being terminated above and below by two flat 

 furfaces, which give attachment to the fibro-cartilages occu- 

 pying the intervertebral fpaces. This body of the vertebra 

 forms in front a greater or lefs convexity, in which we ob- 

 ferve a kind of tranfverfe depreffion, bounded by two promi- 

 nent edges ; it is plane, or a little concave, behind, where it 

 correfponds to the vertebral canal : in both fitnations there 

 are feveral apertures for the paffage of blood-veffels into the 

 fubftance of the bone. At each fide the body is continuous 

 with the re(t of the bone by a kind of pedicle. 



A large oval or triangular opening, called the ring or fora- 

 men, and contributing to the formation of tlie vertebral canal, 

 which holds the medulla fpinalis, is placed immediately behind 

 the body. DireAly behind this opening is the fpinous procefs, 

 varying in form and direftion in the different regions, pro- 

 jefting backwards beyond the level of the bone, and feparated 

 from the correfponding proceffes immediately above and be- 

 low it, by a fpace filled either with iiiufcles or 'igaments. 



Such are the parts of each vertebra as come into notice 

 on the middle line of the bone, from before backwards. 

 When we view it laterally, we obferve, iff, two notclies, a 

 fuperficial one above and a much deeper below, excavated 

 on the pedicle, which connefts the body to the articular and 

 tranfverfe proceffes, and forming, when the bones are joined, 

 thofe lateral foramina of the vertebral canal, through which 

 the nerves are tranfmitted ; 2dly, two articular or oblique 

 procedes, a fuperior and an inferior, furnifhcd with carti- 

 laginous furfaces, by which they are articulated to the corre- 

 fponding proceffes of the bones above and below, and having 

 this furface turned backwards or inwards in the fuperior, 

 forwards or outwards in the inferior ; fo that each vertebra 

 is mechanically locked in its fituation by the two vertebra: 

 immediately above and below it ; its fuperior articular pro- 

 ceffes being overlapped by the inferior ones of the bone 

 above, while its inferior proceffes overlap thofe of the bone 

 next below : 3dly, a tranfverfe procefs, directed horizontally, 

 as its name indicates, longer or fhorter in the different re- 

 gions, and giving attachment to mufcles ; and 4thly, a flat- 

 tened plate, united to that of the oppofite fide to form the 

 fpinous procefs. 



Particular Forms of the Vertebra. — The various common 

 circumftances jult enumerated are greatly modified in the 

 different regions ; it is principally in the middle of each 

 region that we muff examine thefe modifications, which, at 

 either end, gradually approach to the characters of the neigh- 

 bouring region?. 



The Cervical Vertebra. — Their number is very conftantly 

 feven ; but inftances are mentioned, in which there have been 

 eight or only fix. (See Euftachius, Offium Examen, p. 210; 

 and Columbus de Re Anatomica, p 263.) The peculiarities 

 of form are ftrongly marked and diltind in this region. 

 The firft and fecond too, in confequence of their articulation 

 to the head, differ widely from the others, and muff therefore 

 be defcribed feparately. 



The atlas, or firft vertebra of the neck, deviates more 

 than any other from the general type. It is very much ex- 

 panded laterally, and its ring or foramen is very capacious. 

 When we look at it in front, it feems to want the body, in- 



ftead of which we find a fmall bony arc, flattened in an op^ 

 pofite direftion to that of the bodies of the other vertebrae, 

 convex and rifing into a tubercle in front, concave behind, 

 where it bears a fmooth cartilaginous furface, articulated to 

 the odontoid procefs, thin above and below, where it is con- 

 nefted, by means of ligaments, to the occiput and fecond 

 vertebra. Immediately bel)ind this bony arc is the large 

 ring, larger in this than in any bone of the column, and 

 confifting of an anterior fmaller, and a pofterior larger divi- 

 fion, of which the diftinftion is marked by two protuberances, 

 between which a tranfverfe ligament is extended. The front 

 of the ring is filled by the odontoid procefs ; its back 

 part is the beginning of the vertebral canal. Inftead of the 

 fpinous procefs, and of the laminae which unite to form it, 

 there is a polterior bony arc, about twice as large as the an- 

 terior, rifing into a fmall tubercle at the middle, where the 

 fpinous procefs flwuld be, and bounding the vertebral canal 

 behind. The edges of this arc have ligamentous con- 

 neftions above and below. Inftead of articular proceffes, 

 the atlas poffeffes on each fide, above, a large oval cavity, 

 direfted obliquely from behind forwards and inwards, cover- 

 ed by cartilage, eroded by a notch, in which a fynovial 

 gland is placed, more elevated at its outer than at its inner 

 edge, and correfponding to the occipital condyle, with 

 which it is articulated ; below, a large, circular, and nearly 

 horizontal plane, covered by cartilage, and articulated to a cor- 

 refponding plane of the fecond vertebra. A very deep channel, 

 fometimes formed by a bony plate into a complete foramen, is 

 placed immediately behind the fuperior articular concavity ; 

 it is occupied by the vertebral artery, and the firft cervical 

 or fub-occipital nerve. The inferior notch, contributing to 

 the opening for tranfmitting the fecond cervical nerve, is 

 behind the inferior articular plane : thus the nerves, which in 

 all the reft of the fpine go out in front of the articular pro- 

 ceffes, pafs behind them in the atlas. The tranfverfe pro- 

 cefs is very remarkable for its length, much exceeding that 

 of any other cervical vertebra. It is formed by a flender 

 anterior and pofterior root, between which the foramen for 

 the vertebral artery is placed, uniting into a confiderable ob- 

 tufe prominence. Thus the atlas, with the exception of the 

 thick lateral parts, to which the occipital condyles are arti- 

 culated, forms nearly a bony ring. 



To the tubercle of its anterior arch the longus colli and 

 the reftus capitis internus minor are fixed : to the tranfverfe 

 procefs, the reftus lateralis, the obliquus fuperior and in- 

 ferior, the levator fcapula, the intertranfverfi, and the fca- 

 lenus anterior. The reftus pofticus minor is fixed to the 

 tubercle of the pofterior arch. 



The vertebra dentata, axis, epiftropheus, or fecond ver- 

 tebra of the neck, is diftinguiftied from all others by its 

 odontoid or tooth-hke procefs, and by its large, fuperior, 

 articular planes. Its body exhibits above, inftead of the 

 ufual fuperior furface, a large bony procefs, called the den- 

 tiform, odontoid, or tooth-like, having a flightly convex 

 cartilaginous furface in front, articulated to the back of the 

 anterior bony arc of the atlas, a fmall, concave, articular 

 face behind, on which' the tranfverfe ligament plays, and 

 terminating above in a rather unequal obtufe extremity, from 

 which ligaments arife, connefting it to the lateral anterior 

 portions of the foramen magnum. The anterior furface of 

 the body of the axis has a middle line, on each fide of which 

 it is flightly hollowed for the longi colli : the pofterior, 

 rough, and perforated by fmall openings for blood-veffels, 

 forms part of the vertebral canal. The inferior furface gives 

 attachment to the firft intervertebral fibro-cartilage. The ring 

 is as large in this as in the atlas. The plates of the fpinous 



procefs 



