. Quain's elements of anatomy . cond dorsal vertebra ; it islargest opposite the fifth or sixthcervical vertebra, where it measuresfrom 13 to 14 mm. from side to lower or lumbar enlargementbegins at the tenth dorsal vertebra,is largest opposite the twelfth dorsal(11 —13 mm. across), and from thispoint becomes gradually smaller ; itsantero-posterior diameter is more nearlyequal to the transverse than is the casein the cervical eularc-ement. Below EXTEENAL FOEM. 263 the lumbar enlargement the cord tapers in the form of a cone (connsmeduUaris), from the apex of which the small filiform p
. Quain's elements of anatomy . cond dorsal vertebra ; it islargest opposite the fifth or sixthcervical vertebra, where it measuresfrom 13 to 14 mm. from side to lower or lumbar enlargementbegins at the tenth dorsal vertebra,is largest opposite the twelfth dorsal(11 —13 mm. across), and from thispoint becomes gradually smaller ; itsantero-posterior diameter is more nearlyequal to the transverse than is the casein the cervical eularc-ement. Below EXTEENAL FOEM. 263 the lumbar enlargement the cord tapers in the form of a cone (connsmeduUaris), from the apex of which the small filiform prolongation iscontinued downwards. The cervical and lumbar enlarg-ements liave an evident relation to the largesize of the nerves which supply the upper and lower limbs, and which are con-nected mth those regions of the cord. At the commencement of its developmentin the embryo, the spinal cord is destitute of these enlargements, which, in their firstappearance and subsequent progress, correspond with the gro-wth of the Vig. 244.—POSTERIOE VIEW OP THE MEDULLA OBLONGATA AND OP THE SPINAL COKD WITIIITS COVERINGS AND THE ROOTS OF THE NERVES (Sappey). J The theca or dura-matral sheath has been opened by a median incision along the wholelength, and is stretched out to each side. On the left side, in the upper and middle parts{A and B), the posterior roots of the nerves have been removed so as to expose the liga-mentum denticulatum, 9, and the anterior roots, 13 ; and along the right side the pos-terior roots, 10, are shown arising from the postero-lateral groove, and passing out throughthe dura mater. The roman numbers indicate the different nerves in the cervical, dorsal,lumbar, and sacral regions respectively ; 11, posterior median fissure; 12, ganglia onthe posterior roots : 14, the united nerve beyond the ganghon ; 15, tapering lower endof the .spinal cord; 16, filum terminale ; 17, cauda equina. The terminal filament (filum terminale, central ligament) (fig,245, h, h
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