Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/207

 Part I. ANATOMY. 167 or more fluid texture. The middle point is therefore a Though the true vertebra agree in the general ftrucfulcrum or pivot, on which the motion of a ball and ture which we have hitherto defcribed ; yet becaufe of focket may be made, with fuch a gradual yielding of the feveral fpecialities proper to a particular number, they fubftance of the ligament, in whichever diredion our are commonly divided into three clafles, viz. cervical, fpines are moved, as faves the body from violent (hocks, dorfal, and lumbar. and their dangerous confequences. This ligamento- The cervical are the feven uppermoft vertebra ; which cartilaginous fubftance is firmly fixed to the horizontal are diftinguiftied frpm the reft by thefe marks. Their furfaces of the bodies of the vertebrse, to conned them, bodies are fmaller and more folid than any others, and in which it is aflifted by a ftrong membranou^igament, flatted on the fore-part, to make way for the oefophagus; which lines all their concave furface, and uy ftill a or rather this flat figure is owing to the preflure of that ftronger ligament, that covers all their anterior convex pipe, and to the adtion of the longi colli and anterior recti mufcles. They are alfo flat behind, where fmall furface. From each fide of the body of each vertebra, a bony procefles rife, to which the internal ligaments are fixed. The upper furface of the body of each vertebra is bridge is produced backwards, and to a fide ; from the pofterior end of which, one flanting procefs rifes and an-- made hollow, by a (lanting thin procefs which is raifed other defcends ; the fmooth, and what is generally the on each fide :—The lower furface is alfo excavated, but flatteft fide of each of thefe four procefles, which are in a different manner; for here the pofterior edge is raicalled the oblique, is covered with a fmooth ,cartilage; fed a little, and the ohe before is produced a confiderand the two lower ones of each vertebra, are fitted to, able way. Hence we fee how the cartilages between and articulated with the two upper or afcending oblique thofe bones are firmly connedted, and their articulations procefles of the vertebra below, having their articular are fccure. The cartilages between thefe vertebrae are thick, eligaments fixed into the rough line round their edges. From between the oblique procefles of each fide the fpecially at .their fore-part; which is one reafon why vertebra is ftretched out laterally into a procefs that is the vertebra advance forward as they defcend, and have larger motion. named tranfverfe. From the back-part of the roots of the two oblique, The oblique procefles of thefe bones of the neck more and of the tranfverfe procefs of each fide, a broad ob- juftly deferve that name than thofe.of any other vertebra. lique bony plate is extended backwards, where thefe They are fituated (lanting; the upper ones having their meet, the feventh procefs of the vertebra takes its rife, fmooth and almoft flat furfaces facing obliquely backand (lands out backwards: This being generally (harp wards and upwards, while the inferior oblique proceiTes pointed, and narrow edged, has therefore been called have their furfaces facing obliquely forwards and downfpinal procefs ; from which this whole chain of bones wards. has got its name. The tranfverfe. procefles of thefe vertebra are framed Befides the common ligament which lines all the in- in a different manner from thofe of any other bones of ternal furface of the fpinal procefles, as well as of the the fpine : For befides the common tranfverfe procefs bodies, there are particular ligaments that connect the riling from between the oblique procefles of each fide, bony bridges and procefl'es of the contiguous vertebra to- there is afecond one that comes out from the fide of the gether. body of each vertebra; and thefe two procefies, after The fubftance of the procefles is confiderably ftronger leaving a circular hole for the paflage of the cervical arand firmer, and has a thicker external plate than the bo- tery and vein, unite, and are confiderably hollowed at dies of the vertebra have. their upper part, with rifing (ides, to protedt the nerves The feven procefles form a concavity at their fore- that pafs in the hollow; and at laft each fide terminates part, which, joined to the one at the back-part of the in an obtufe point, for the infertion of mufcles. bodies, makes a great hole, and the holes of all the ver- The fpinal procefles of thefe cervical bones (land tebrse form a long large conduit, for containing the fpi- nearly (freight backwards, are (horter than thofe of any nal marrow. In the upper and lower edge of each la- other vertebra, and are forked or double at their ends ; teral bridge, there is a notch. Thefe are fo adapted to and hence allow a more convenient infertion to mufcjes. each other in the contiguous vertebra, as to form a So far moft of the cervical vertebra agree ; but they round hole in each fide between each two vertebra, have fome particular differences, which oblige us to conthrough which the nerves that proceed from the fpinal (ider them feparately. marrow and its blood-veflels pafs. The firft, from its ufe of fupporting the head, has the The articulations then of thefe true vertebra are name of atlas ; and is alfo called epijlropkea, from the plainly double ; for their bodies are joined by the inter- motion it performs cn the fecond. vening cartilage above defcribed, and their oblique pro- The atlas, contrary to all the other vertebra of the cefles being tipped with cartilages, are fo connedted by has no body; but, inftead of it, there is a bony their ligaments, as to allow a finall degree of motion to fpine, arch. In the convex fore-part of which, a fmall all (ides. rifing appears, where the muiculi longi colli are inferrThe true vertebra ferve to give us an eredt pofture ; ed ; and, on each fide of this protuberance, a fmall cato allow fufficient and fecure motion to the head, neck, vity may be obferved, the redi interni minores and trunk of the body, and to fupport and defend the take their rife. Thewhere upper and lower parts of the bowels, and other foft parts. arch are rough and unequal, where the ligaments that conned