John Herbert Parsons.

The pathology of the eye (Volume 3) online

. (page 18 of 37)
Online LibraryJohn Herbert ParsonsThe pathology of the eye (Volume 3) → online text (page 18 of 37)
Font size
QR-code for this ebook


of 0*5 I'o D, or in seven eighths of 0^25 1*25 D. In 95*7 per cent, of
children the axes were according to the rule. The frequency of astig-
matism against the rule increases gradually to the seventieth year, and
afterwards more rapidly. Schon found the percentage of eyes with
inverse astigmatism increase from ii'6 per cent, in youth to 68*3 per
cent, in old age. Hess found scarcely i per cent, of cases of astigma-
tism from 6 to 14 years of age against the rule ; in the same period
there was no decrease in direct astigmatism : in 10 12 per cent, of all
children the total astigmatism amounted to at least i D. Nordenson
found in school children 77 per cent, direct, 1*3 per cent, indirect, astig-
matism ; 12 per cent, with oblique axes, 4*4 per cent, without corneal
astigmatism ; 30 per cent, had astigmatism of at least i D, 1*7 per cent,
more than i'5 D. Pfluger found astigmatism against the rule more
common in females u : 9 ; according to Steiger astigmatism is gene-
rally somewhat greater in women than in men. In most cases the axes
are symmetrical in the two eyes 1307 : 458 cases (Risley and
Thorington). The difference in refraction between the two meridians
seldom exceeds 5 6 D : rare cases in which cylinders of 10 D and
even 20 D have been worn are reported (Schneidernann, Despagnet).

The ordinary forms of astigmatism must be regarded as a congenital
anomaly. The influence of the intra-ocular pressure upon the corneal
curvature has been often investigated (Schelske, Laqueur, Eissen,
Bajardi, Lucciola). Helmholtz found that the corneal curvature was
greater in excised eyes than in the living eye, and that the cornea
became flatter on injecting water into the vitreous chamber. These
observations were confirmed on animals' eyes by Schelske and Laqueur,
who found that all diameters were increased. The results were not,
however, constant, for Schelske found that the corneal radius, after
increasing for a time, became diminished on further increasing the
pressure ; it then remained constant awhile, again increasing with the
greater pressures. Eissen showed that in rabbits a rise of tension of
5 lomm. often, and of 25 mm. constantly, caused changes. Usually
all meridians were altered ; with gradual increase of pressure astigma-



HYPERMETROPIA AND ASTIGMATISM 937

tism at first increased, then diminished, so that a normal astigmatism
might give place to an inverse. Astigmatism against the rule has
frequently been observed in human glaucomatous eyes, in 41 50 per
cent, as compared with 2'2 per cent, in normal eyes (Schon, Pfalz,
Martin). The cause of the change in astigmatism with increasing
age is unknown. Eissen attributed it to change in tension, Schon to
the influence of partial contraction of the ciliary muscle upon the shape
of the cornea, v. Reuss in 1877 conjectured that contraction of the
ciliary muscle could alter the curvature of the cornea ; he found that
under strong eserin there was a diminution in the radius of the cornea
of 0*04 0*14 mm. Carhart considered that strong efforts of accommo-
dation in a sound eye or ordinary accommodation in a weak eye
might produce stretching of the walls, leading to lengthening of the
axis and changes in the curvature of the cornea. Steiger pointed out
that the constancy of the astigmatism in the plastic eyes of young
children was against this view. Gullstrand found in myopia extreme
variations in the corneal curvature which might be attributed to
stretching of the globe.

Partial contraction of the ciliary muscle has been invoked to
account for the difference between the corneal and the total astigma-
tism. Change in astigmatism with variations in the pupillary diameter
have been held to support the theory. The view has been upheld by
Giraud-Teulon, Dobrowolski, Woinow, Martin, Pfliiger and Mauthner,
and others, whilst it has been opposed by Bull, Sulzer, Tscherning,
Eriksen, Hess, and others. Hess points out many faults in the methods
of observation e.g. the size of the object, movement of the eye, the
effect of the lids as a stenopoeic slit, etc. That lid-pressure can cause
change in the corneal curvature was shown by Botwinnik. and con-
firmed by Bull, Gullstrand, and Howe. It is not improbable that this
is a factor in the pathogenesis of astigmatism. Even stretching the
lids with the finger can effect a considerable change in the cornea, as
shown ophthalmometrically by Laqueur (1884) and Weiss (1886).

Schon, Javal, Roure, Vacher, and others have conjectured an aetio-
logical relationship between astigmatism, and especially partial ciliary
contraction, and cataract formation. Thus in unequal astigmatism the
more affected eye has been said to become cataractous sooner and the
cataract is said to progress more rapidly. Schon's statement that
equatorial cataract begins in the horizontal meridian is denied by Hess.

A form of regular astigmatism following wounds, especially extrac-
tion and iridectomy w r ounds, was first described by Bonders (1864).
With superior or inferior sections it is usually against the rule, as was
pointed out by Haase. The larger the wound-' and the nearer the
middle of the cornea, the greater is usually the astigmatism. It is more
marked and less regular when normal healing is interfered with, as by
prolapse of iris, etc. Exact ophthalmometric observations on wound
astigmatism were first made by v. Reuss and Woinow (1869), later by
Mauthner, Dolganoff, Pfingst, Scimeni, Treutler, and others. Treutler
in 49 cases seven days after extraction found the vertical meridian
diminished in 88 per cent., unchanged in 2 per cent., increased in 10
per cent. ; the horizontal meridian was increased in 88 per cent., un-



938 THE PATHOLOGY OF THE EYE

changed in 2 percent., diminished in 10 percent. The highest diminu-
tion in the radius of the vertical meridian was 1*5 mm., the highest
increase in the horizontal more than r8 mm. The following mean
changes are given :

Vertical meridian. Horixontal meridian.

v. Reuss . 0*3 mm. . 0*27 mm.

Weiss . . 0*45 ,, . o'O2 ,,

Dolganoff 0*44 -0-47

Treutler . 0*7 ,, . i'i ,,

The smaller results obtained by v. Reuss, Weiss, and Dolganoff are
probably due to the length of time after operation 13 to 16 days.
The astigmatism is greatest soon after operation, diminishes rapidly at
first, then very slowly. Treutler found a change still going on after
four months. As the final result Dolganoff found the horizontal
meridian in 18 cases increased 2*2 D, in 2 cases diminished 0*25
o - 5 D ; the vertical meridian was unchanged in 3 cases, increased
0*25 1*25 D in 4, diminished on an average 1*7 D in 13. As Hess
points out, these observations upon wound astigmatism confirm his
investigations of striate opacity (v. Vol. I, p. 180).

Regular astigmatism may occasionally follow wounds other than
those made by operation, and also ulcers. Hirschberg, Dufour, and
Evers have described it after episcleritis or sclerosing keratitis.

In irregular astigmatism the refracted rays have no planes of sym-
metry. The condition is usually due to the irregular shrinking of
scars such as are caused by ulcers or lacerated wounds. It may also
be due to keratoconus, lenticonus, etc.

*THOMAS YOUNG. Phil. Trans., Ixxxiii, 1793 ; CEuvres ophth. de T. Young par Tscher-
ning, Copenhague, 1894. GKRSON.- See K. M. f. A., iv, 1866. AIRY. Cambridge Phil.
Soc. Trans., 1827. HAMILTON. Roy. Irish Acad. Trans., xv, 1828; xvi, 1831; xvii, 1837.
STURM. Jl. de Math., 1838; Comptes rendtis, xx, 1845. SCHUI.TKN. Mem. de 1'Acad.
imperiale de St. Petersbourg, iv, 1845. WHARTON JONES. Proc. Roy. Soc., x, 1860.
BONDERS. A. f. O., vii, 1861 ; Asligmatismus, Berlin, 1862; Anomalien der Refraction
u. Accommodation, Wien, 1866. JAVAL. Ann d'Oc., liii, 1863; Soc. de Biol., 1873, 1879;
Ann. d'Oc., Ixxxvii, Ixxxviii, 1882; xcvii, 1887; Mem. d'Ophtalmometrie, Paris, 1891.
KXAPP. A. f. O., viii, 2, 1866; Ophth. Rev., 1887; T. Am. O. S., 1892; Z. f. A., ii, 1899.
DOBROWOLSKI. A. f. O., xiv, 3, 1868. v. REUSS AND WoiNOW. Ophthalmometrische
Studien, Wien, 1869. WOINOW. A. f. O., xv, 2, 1870; K. M. f. A., ix, 1871. HULKE.
R. L. O. H. Rep., viii, 1875. SCHON. B. d. o. G., 1877; Die Funktionskrankheiten des
Anges, Wiesbaden, 1893. WEISS. A. f. A., vi, 1877; Ann. ri'Oc., cxv, 1896. LEROY.
Comptes rendus, xc, 1880; A. d'O., i, 1881 ; Rev. gen. d'O., 1882; Arch.de Physiol., xxi,
1889. SCHIOTX.. Congres d'O., Milan, 1881 ; A. f. A., xv, 1885. MATHIESSEN. Centralz.
f. Opt. u. Mech., 1882; K. M. f. A., xxi, 1883; A. f. O., xxix, i, 1883; Pfliiger's Archiv,
xxxii, 1883. MARTIN. Ann. d'Oc., xc, 1883; xci, 1884; A. d'O., v, 1885; Ann. d'Oc., xciii,
1885; xcv, 1886; xcvii, 1887; ciii, 1890: cxiii, 1895. NORDENSON. Ann. d'Oc., Ixxxix, 1883.
PKAI.X. C. f. A., ix, 1885; A. f. O., xxxi, i, 1885; Internal. Congress, Utrecht, 1899;
Ophth. Klin., 1899. PRIKSTI.KY SMITH. Ophth. Rev., iv, 1885. THEOBALD. T. Amer.
O. S., 1885. CHIBRET. Ann. d'Or., xcv, 1886; A. d'O., x, 1890; xiv, 1894; Soc. franc. d'O.,
1804. v. HELMHOLTX.- A. f. O., i, 2, 1855. SCHEI.SKE. A. f. O., x, 2, 1864. LAQUEUR.
A. f. O., xxx, i, 1884. EISSEN A. f. O., xxxiv, 2, 1888. EMERSON. T. Amer. O. S.,
1888. EXNKR. A. f. O., xxxiv, i, 1888. IMBERT Gay., hebd., 1888. AHRENS K. M. f. A.,
xxvii. 1889. BUM.. Rev. gen. d'O., 1889; B. d. o. G., 1892: A. d'O., xvi, 1856. SCIMENI.
Ann. di Ott., xviii, 1889. *Gb'LLSTRAND. Skand. Archiv f. Physiol., ii, 1890; A. f. O., liii, 2,
1901. PFI.UGER. Internal, med. Congr., Berlin, 1890. BAJARDI.- Atenea med. Parmense,
iv, 1891 ; Ann. di Ott., xxii, 1893. SULXKR. Soc. fran9_ d'O., 1891. HARI.AN. T. Am.
O. S., 1892; A. of O., xxii, 1893. AXENFEI.D. K. M. f. A., xxxi, 1893. G. J. BULL.
Internal. Congress, Edinburgh, 1894. DOLGANOFF. A. f. A., xxix, 1894. HESS AND



HYPERMETROPIA AND ASTIGMATISM 939

DIEDERICHS. A. f. A., xxix, 1894. HOWE. Amer. Jl. of O., 1894. STEIGER. A. f. A.,
xxix, 1894; xxxvi, 1897; Korrespondenzbl. f. Schweizer Aerzte, 1897. AXTOXELLI. Ann.
di Ott., xxiv, 1895. IACKSOX. Med. News, 1895. ROURE. A. d'O., xv, 1895. *HESS.
A. f. O., xlii, 2, 1896; xliii, i, 1897: in G.-S., viii, 2, 1903 (Bibliography). PFIXGST.
A. of O.. xxv, 1896. RISLEV AXD THORIXGTOX. Jl. of Amer. Med. Assoc., 1896. ASCH-
HEIM. K. M. f. A., xxxv, 1897. D'AuBiGXE-CARHART. New York Med. Jl., 1897.
DESPAGXET. Ann. d'Oc., cxviii, 1897. ELLIS. A. f. A., xxxiv, 1897. CRADLE. A. f. O.,
xliii, i, 1897. EVERS. K. M. f. A., xxxvi, 1898. LANS. A. f. O., xlv, i, 1898. SWAN
BURNETT. Amer. Jl. of O., 1899. CLARK. Ophth. Rev., 1899. REYMOXD. Internal.
Congr., Utrecht, 1899; Z. f. A., ii, 1899. SCHXEIDEMAXX. Ophth. Rev., 1899. AWER-
BACH. Ges. d. Augenarzte, Moskati, 1900.



CHAPTER XVII
THE CIRCULATION OF THE EYE



Arteries. The ocular blood supply in man is derived almost entirely
from the internal carotid artery, whilst it is within the skull. This is
not the case in lower mammals ; and as all experimental investigation
must be made upon these, it is essential to determine accurately the
differences which obtain.

The general tendency as we ascend the animal scale is for the
principal ophthalmic artery, which in the lower members is derived
from the external carotid, to be derived from the internal carotid. On
the border line there are usually two or more ophthalmic arteries
generally one derived from each source, and there is commonly an
anastomotic branch linking the two systems. It is only to be expected
that individual variations should be of frequent occurrence, and such is
the case.

Rabbit. The common carotid in the rabbit gives off the thyroid
artery and the ascending pharyngeal (Fig. 666). At the level of the
hypoglossal nerve the artery divides into the internal and external
carotids. The former is much the smaller, runs without branching to
the bulla tympani, and enters the skull by the carotid foramen. It then
winds round the lateral side of the body of the sphenoid bone, and after
crossing the oculo-motor nerve, gives off the anterior communicating
and superior ophthalmic arteries. It ends by dividing into the anterior
and middle cerebral. In four out of six dissections one was able to
trace a fine branch of communication between the internal carotid, as
it lies on the side of the body of the' sphenoid, and the internal maxillary
close to the origin of the inferior ophthalmic artery. The external
carotid gives from its inner side the laryngeal, lingual, and external
maxillary in that order from below upwards. The last-named artery
gives off the facial. From the posterior wall is given off the occipital.
A little below the neck of the jaw the artery divides into the superficial
temporal and the internal maxillary. The former gives off the transverse
facial and the auricular. The internal maxillary runs deep to the
internal pterygoid behind the lower jaw. It gives off the tympanic,
the inferior alveolar, some muscular branches, and the middle menrn-
geal. It then passes through the pterygoid canal, and gives off the



THE CIRCULATION OF THE EYE 941

inferior ophthalmic. It ends by supplying a superior alveolar branch
and divides into the infra-orbital and pterygo-palatine arteries.

So far in these dissections the arrangement of the branches of the
carotid arteries is in entire agreement with the description given by
Krause. I have therefore followed his nomenclature. I now quote in
full his description of the ophthalmic arteries (Fig. 667).

" The inferior ophthalmic artery runs on the anterior surface of the
upper part of the great wing of the sphenoid, bends forward over the
optic nerve, and reaches its anterior side. It then anastomoses with the
superior ophthalmic artery. Its branches are as follows : (i) Lacrymal,
which appears through the posterior supra-orbital foramen as the supra-
orbital artery. (2) Frontal, which in the same way goes through the
anterior supra-orbital foramen. Immediately after its origin it usually
gives off the well-developed anterior ethmoidal artery which goes through




FIG. 666. SCHEME OF THE CAROTID ARTERIES IN THE RABBIT.
Henderson, R. L. O. H. Rep., xv. A. Common carotid artery. B. Thyroid
artery. E. Laryngeal artery. F. Ascending pharyngeal artery. G. Internal carotid
artery. H. Occipital artery. I. Lingual artery, j. External maxillary artery.
K. Internal maxillary artery. L. Transverse facial artery. M. Superficial temporal
artery. N. Auricular artery, xn. Hypoglossal nerve. I. Placed on the bulla tympani.
2. On the lower jaw.

the ethmoidal foramen into the nasal cavity. (3) Muscular branches to
the eye muscles.

The superior ophthalmic artery is but little developed. It runs
forward to the optic foramen, and goes through this on the under and
lateral side of the optic nerve into the orbit, winds under the nerve to
its anterior side, and anastomoses with the inferior ophthalmic artery.
It gives off the ciliary arteries and the central artery of the retina."
(Krause.)

In two of the dissections there was no anastomosis between the two
ophthalmic arteries in the situation here described. In both these cases
the anastomotic branch between the internal carotid and the inferior
ophthalmic was present. In two others this anastomotic branch was
also present, and in these the superior ophthalmic artery was very small.



942 THE PATHOLOGY OF THE EYE

Dog. In the dog the carotid artery gives off as its first branch a
thyroid artery (Fig. 668). A muscular branch to the sternomastoid
usually arises at about the same level as the thyroid. A little higher
the ascending pharyngeal and the laryngeal arise. The artery now
divides into the internal and external carotids. The internal carotid is
always the first postero-external branch (Fig. 669). It takes origin
just at the level of the hypoglossal nerve. It is most easily reached in
the living animal by retracting the common carotid outwards, and
tracing up its inner side. There is always present an enlargement close
to its origin.

The artery runs straight up with the vagus to the bulla, and enters
the skull through the carotid foramen. It gives no branches in the
neck. The external carotid gives as its first branch on the outer side




FIG. 667. SCHEME OF THE INTERNAL MAXILLARY AND OPHTHALMIC ARTERIES

OF THE RABBIT.

Henderson, R. L. O. H. Rep., xv. A. External carotid artery. B. Tympanic
artery, c. Superior alveolar artery. G. Internal carotid artery. K. Internal maxillary
artery. M. Superficial temporal artery. N. Auricular artery, o. Inferior alveolar
artery. p. Muscular arteries. Q. Middle meningeal artery. R. Ramus anasto-
moticus. T. Ethmoidal artery, u. Lacrymal artery, v. Frontal artery, w. Supe-
rior ophthalmic artery, x. Inferior ophthalmic artery. Y. Infra-orbital artery.
/.. Pterygopalatine artery, i. Placed on the pterygoid canal.

the occipital. This artery arises close to the internal carotid, and is of
about the same size. In the living animal it may be readily mistaken
for it. It is somewhat more superficial in origin, and will usually be
found to give an anterior branch soon after its origin. The next branch,
and one of the largest, is the lingual. Then conies the external maxil-
lary, from which is derived the facial. The artery then breaks up into
the superficial temporal, auricular, and internal maxillary arteries. The
internal maxillary winds round the maxillary joint over the bulla, enters
the pterygoid canal, and ends after leaving this by dividing into the
infra-orbital and palatine branches. Its branches may be divided into
two sets : those given off before it enters the pterygoid canal, and those
given off after it leaves it. The first set comprise the middle meningeal,
the deep temporals, the inferior alveolar, and the muscular. The



THE CIRCULATION OF THE EYE



943



second set comprise a further set of muscular branches and the inferior
ophthalmic (Fig. 670).

" The ophthalmic artery springs from the internal maxillary after it




has left the pterygoid canal, and next runs between the peri-orbita and
the temporal muscle, and further in on the orbital part of the frontal
bone on the outer side of the peri-orbita to the ethmoidal foramen.
Through this it runs into the skull as the ethmoidal artery. Shortly



THE PATHOLOGY OF THE EYE

after its origin it, or one of its muscular branches, gives an anastomotic
branch, which goes to the internal carotid. This, according to Bellar-
minow, who calls it the internal ophthalmic artery, gives off the central
artery of the retina." (Ellenberger and Baum.)

In none of our dissections has this arrangement been exactly followed
(Figs. 671, 672, and 673). In all of them the anastomotic branch from
the internal carotid has entered the internal maxillary immediately before
the origin of the inferior ophthalmic artery, and this latter has in all
been represented by two separate branches. In consideration of the
conditions found in the rabbit it is wiser to adhere to the terms
" superior " and " inferior," although Bellarminow's division into internal




FIG. 669. SCHEME OF CAROTID ARTERIES IN THE DOG, TRACED HIGHER AFTER

DIVISION OF THE DIGASTRIC.

Henderson, R. L. O. H. Rep., xv. A to N. As in Fig. 668. i. Placed on the
digastric. 2. On the ear. 3. On the bulla tympani. 4. On the lower jaw.

and external has the advantage of indicating their source from the
internal and external carotids respectively. In only half the dissections
has there been present a superior ophthalmic artery arising from the
ramus anastomoticus. In the remaining half this artery has been
derived from the internal carotid after the main trunk has left the
internal carotid, and has entered the orbit through the optic foramen.
The anastomotic branch is always of very fair size, and arising imme-
diately after the internal carotid has reached the cavernous sinus, passes
through the fissura orbitalis below the first division of the fifth nerve.
In two dogs a large meningeal branch has arisen from the ramus anas-
tomoticus on both sides. This branch has apparently taken in these
cases the place of the middle meningeal.



THE CIRCULATION OF THE EYE



945



If the anastomotic branch always supplied the interior of the eye it
is certainly of sufficient size to maintain the circulation, and as blood
reaches it equally from the internal maxillary and internal carotid, it is
probable that the supply to the eye would not suffer from the loss of
only one of these sources. This, however, as has been shown, is not
invariably the case. But in those cases in which the ciliary arteries
and the central artery of the retina have been derived from a superior
ophthalmic artery arising from the internal carotid a free anastomosis
has always been present between this superior ophthalmic artery and




r




FIG. 670. SCHEME OK INTERNAL MAXILLARY AND OPHTHALMIC ARTERIES

IN THE DOG.

Henderson, R. L. O. H. Rep., xv. K. Internal maxillary artery, o. Inferior
alveolar artery. P. Deep temporal artery. Q. Middle meningeal artery. R. Ramus
anastomoticus. s, Superior ophthalmic artery (inferior of Bellarminow). T. Eth-
moidal artery. u. Lacrymal artery. v. Frontal artery, v', v", v"'. The three
parts of the fifth nerve, i. Placed on the eye. 2. On the temporal and pterygoid
muscles, cut and turned down. 3. On the masseter, also turned down. 4. On the
lower jaw. 5. On the bulla tympani. 6. On the ear. 7. On the pterygoid canal.

one of the branches of the inferior ophthalmic artery. It is, then, even
in these cases, anatomically possible for the intra-ocular circulation to
be maintained in the absence of one or other of the ophthalmic arteries.
Man. In man the arteries to the eye are derived almost exclusively
from the internal carotid artery as it lies within the skull. It is
unnecessary in this place to enter into details as to the origin and



THE PATHOLOGY OF THE EYE

distribution of the various branches in their course outside the eye (see
Quain's 'Anatomy,' Figs. 344, 345).

FIG. 671.




FIG. 672.




FIG. 673.




FIGS. 671, 672, AND 673. VARIATIONS IN THE ORBITAL ARTERIES IN THE DOG.
Henderson, R. L. O. H. Rep., xv. G. Internal carotid. K. Internal maxillary
artery. y. Middle meningeal artery. R. Ranius anastomoticus. w. Superior
ophthalmic artery. x. Inferior ophthalmic artery. T. Ethmoidal artery. u.
Lacrymal artery, v. Frontal artery.

The anastomoses between branches of the ophthalmic artery and
those of the external carotid are very few and very small. On the
authority of Quain's ' Anatomy ' :



THE CIRCULATION OF THE EYE . 947

(i) The central artery of the retina usually arises in common
with the internal ciliary trunk, sometimes with the external. No
anastomoses. (2) Ciliary arteries : (a) posterior from ophthalmic ;
(b) anterior from muscular and lacrymal. The former have no
anastomoses and the latter no direct one. (3) Lacrymal. This
anastomoses with the anterior deep temporal and transverse facial, and
through the outer end of the sphenoidal fissure with the middle
meningeal. (4) Recurrent branch to anastomose with internal carotid.
(5) Muscular branches. Some anastomoses between the infra-orbital
and these branches must take place in the substance of the inferior
oblique, but are not directly mentioned. (6) Supra-orbital. This
anastomoses with superficial temporal. (7) Anterior and posterior
ethmoidal. No anastomoses given. (8) Palpebrals. No anastomoses
given. (9) Nasals. Anastomose with facial. (10) Frontals. No
anastomoses given.

The following variations are also enumerated. The ophthalmic
artery may enter the orbit through the sphenoidal fissure. The lacry-
mal artery not infrequently, and in rare cases a large part, or even the
whole, of the ophthalmic artery itself arises from the middle meningeal.
The lacrymal artery may also be reinforced by the anterior deep
temporal artery. The ophthalmic artery has been seen to give off the
middle meningeal.

Fr. Meyer, in discussing a case in which an abnormal course of the
branches of the ophthalmic artery led to free arterial bleeding, and in
which a subsequent post-mortem examination showed that the lacrymal
and frontal arteries were derived by a common stem from the middle
meningeal, sums up the literature of the subject and enumerates the
possible varieties. There is, however, no mention made of the morpho-
logy. In view of the conditions found in the animals now under
discussion, the occasional origin of the ophthalmic artery, or of some of
its branches, from the middle meningeal may be of morphological
importance.

Veins. Whilst the arterial anastomoses in man are few and probably
insignificant, the venous anastomoses are large and of great physio-
logical importance throughout the mammalia. Even here, however,



Online LibraryJohn Herbert ParsonsThe pathology of the eye (Volume 3) → online text (page 18 of 37)