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 Fart VT. A N A 1 Tome of them lie very near the fldn, and the reft at a greater diftance from it. As thefe lymphatic glands differ more in fituation than in fize or figure, they are commonly enumerated and denominated from the places where they lie; e. g. Glandular parotides lymphaticae, Glandulse maxillares lymphaticse, Glandule jugulares, &c. The lymphatic veffels were difcovered more than an ■hundred years.ago. But their nature and origin were not underflood till Dr Alexander Monro, prefent Profeffor of Anatofhy in the Univerfity of Edinburgh, publifhed his treatife, De Venis Lymphaticis Valvulofis, in the year 1757. In this treatife the. Dodtor has pioved, by many accurate experiments. That the lymphatic veflels are a fyftem of abforbents: That they are not continuations of the arteries or veins ; but that they are a diftindl fyflem of veffels, deftined for abforbing a pellucid liquor called lymph, from the different cavities .of the body, be. and for tranfmitting it to the blood, by the contradlion

O- M Y. 309 of their coats, and the preffure of the neighbouring parts. Befides thefe veffels which accompany the glands, there are others of the fame ftrudture found on the feveral vifeera, where no lymphatic glands have hitherto been difcovered. We meet with them in very great numbers in the external membrane of the liver, and in the duplicature of the fuperior membranous ligament of this vifeus. Another fort of veffels termed lyjnphatics, are the fmall arteries and veins, which, in the natural (late, tranfmit only the ferous part of the blood. Thefe veffels differ from the abforbent lymphatics in the fmallnefs of their diameter, and in their llrudlure and fituation. All thefe little arteries and veins are uniform, extremely narrow; and though their fides are not thinner than thofe of the valvular lymphatics, yet their diameters are generally lefs. The other lymphatics are full of valves, and very thin, but they are not narrow in proportion. The arterial and venal lymphatics are found on the parts which are naturally white, as on the /kin, the white of the eye, be.

EXPLANATION Figure x. Shews the lachrymal canals, after the common teguments and bones have been cut away. a. The lachrymal gland, h, The two pundta lachrymalia, from which the two lachrymal canals pnoceed to c, the lachrymal fac. d, The large hchrymal du<ft. e. Its opening into the nofe. f, The caruncula lachrymalis. g, The eye ball. Fig. 2. An anterior view of the coats and humours of the eye. a a a a, The tunica fclerotica cut in four angles, and turned back, b b b b. The tunica choroides adhering to the infide of the fclerotica, and the ciliary vefiels are feen paffing over'—c c, The retina, which covers the vitreous humour. d d, The ciliary proceffes, which were continued from the choroid.coat. e e. The iris, f, The pupil. Fig. 3. Shews the optic nerves, and mufcles of the eye. a a. The two optic nerves before they meet, b, The two optic nerves conjoined, c, The fight optic nerve. d, Mufculus attollens palpebrae fuperioris. e, Attollens'oculi. f, Abdudlor. g g, Obliquus fuperior, or trochlearis. h, Addudtor. i. The eye-ball. Fig. 4. Shews the eye-ball with its mufcles. a, The optic nerve, b, Mufculus trochlearis. c, Part of the os frontis, to which the trochlea or pulley is fixed, through which,—d. The tendon of the trochlearis paffes. e, Attollens qculi. f, Addudtor oculi. g,’ Abduftor oculi, h, Obliquus inferior, i, Part of riie fupepior maxillary bone to which it is fixed, k. The eye-ball. Vol. I. No. 13. 3

of PLATE XXI. Fig. 5. Represents the nerves and mufcles of the right eye, after part of the bones of the orbit have been cut away. A, The eye-ball. B, The lachrymal gland. C, Mufculus abdudtor oculi. D, Attollens. E, Levator palpebrae fuperioris. F, Depreffor oculi. G, /ddudtor. H, Obliquus fuperior, with its pulley. I, its infertion into the felerotie coat. K, Part of the obliquus inferior. L, The anterior part of the 03 frontis cut. M, The cry/la galli of the ethmoid bone. N, The po/lerior part of the fphenoid bone'. O, Tranfverfe fpinous procefs of the fpenoid bone. P, The carotid artery, denuded where it paffes thro’ the bones. Q, The carotid art'ery within tire cranium. R, The ocular artery. Nerves.—a a, The optic nerve, b. The third pair.—c, Its joining with a branch of the fir/l branch of the fifth pair, to form 1, The lenticular ganglion, —which fends off the ciliary nerves, d. e e. The fourth pair, f. The trunk of the fifth pair, g, The fir/l branch of the fifth pair, named ophthalmic. h. The frontal branch from it. i, I ts ciliary branches, along with which the nafal twig is fent to the nofe! k. Its branch to the lachrymal gland. 1, The lenticular ganglion, m, The fecond branch of the fifth pair, named fuperior maxillary, n. The third branch of the fifth pair, named inferior maxillary, o. The fixth pair of nerves,—which fends off p. The berinning of the great fympathetic. q. The remainder°of the fixth pair, fpent on c, The abdurior oculi. Fig. 6. Reprefents the head of a youth, where the upper part of the cranium is fawed off.—to fliew the upper part of the brain, covered by the pia mater, the veffels of which are minutely filled with wax. A A, The cut edges of the upper part of the cranium. 4I B, The