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roof of the upper part of the posterior triangle, to its termination in the external jugular vein.

As the external jugular vein pierces the deep cervical fascia in the subclavian triangle, its wall is closely attached to the margin of the opening through which it passes ; and as it is crossing in front of the third part of the subclavian artery it is joined by the transverse scapular, transverse cervical, and anterior jugular veins.

There are usually two valves in the lower part of the vein-one, at its termination, which is generally incompetent, and a second at a higher level.

Tributaries. In addition to the posterior auricular vein and the branch from the posterior facial vein by which it is formed, the external jugular vein receives the posterior external jugular vein, which has already been described, the transverse cervical and transverse scapular veins from the region of the shoulder, and the anterior jugular vein. Occasionally the cephalic vein also opens into it.

The posterior auricular vein (Fig. 785) receives tributaries from the posterior parts of the parietal and temporal regions and from the medial surface of the auricle. It is considerably larger than the posterior auricular artery, which it accompanies only in the scalp. At the base of the scalp it leaves the artery and descends in the superficial fascia, over the upper part of the sterno-mastoid, to join the external jugular vein.

The transverse cervical and transverse scapular veins accompany the corresponding arteries; not infrequently they open directly into the subclavian vein.

The anterior jugular vein commences in the submental region, and is formed by the union of small veins from the lower lip and chin. It descends, in the superficial fascia, at a variable distance from the median plane, perforates the superficial layer of the deep fascia, a short distance above the sternum, and enters the suprasternal space (Burns) between the first and second layers of the deep fascia. In the space it anastomoses with its fellow of the opposite side and receives a communication from the common facial vein. Then it turns laterally, between the sterno-mastoid superficially and the sterno-hyoid, sterno-thyreoid, and scalenus anterior muscles deeply, and terminates in the external jugular vein at the posterior border of the sterno-mastoid.

The external jugular vein sometimes receives the occipital vein or a communication from it.

THE VEINS OF THE SCALP.

The veins which drain the blood from the superficial parts of the scalp are the frontal, the supra-orbital, the superficial temporal, the posterior auricular, and the occipital. The blood from the deeper part of the scalp, in the region of the temporal fossa, on each side, passes into the deep temporal veins, which are tributaries of the pterygoid plexus.

The frontal and supra-orbital veins receive blood from the medial and anterior part of the scalp. They unite together, near the medial commissure of the eyelids, to form the angular vein; before the union is effected the supra-orbital vein sends a branch backwards, through the supra-orbital notch, into the orbital cavity, where it terminates in the ophthalmic vein, and as this branch passes through the notch it receives the frontal diploic vein (p. 969).

The superficial temporal vein (Figs. 759, 785) is formed by frontal and parietal tributaries which accompany the corresponding branches of the superficial temporal artery. They drain the lateral frontal, the superficial part of the temporal, and the anterior part of the parietal region of the scalp, and unite to form a single trunk which descends to the upper border of the zygoma, immediately anterior to the auricle, where it terminates in the posterior facial vein (see p. 968).

The posterior auricular vein drains the posterior portions of the temporal and parietal areas of the scalp (see above).

The occipital vein (Figs. 759, 785) receives tributaries from the parietal and occipital regions. As a rule it pierces the occipital origin of the trapezius, and, passing into the sub-occipital triangle, terminates in a plexus of veins which is drained by the vertebral and deep cervical veins. It sometimes communicates with the external jugular vein, and occasionally an offset from it accompanies the corresponding artery and ends in the internal jugular vein.

It generally receives the mastoid emissary vein; one of its tributaries receives the parietal emissary vein, and occasionally an emissary vein from the confluens sinuum (0.T. torcular Herophili) opens into it.

THE VEINS OF THE ORBIT, THE NOSE, AND THE INFRA-TEMPORAL REGION.

The veins of these three regions are closely associated together; for although the orbital blood is returned, for the most part, to the cavernous sinus, by the ophthalmic vein, the latter vein is closely connected with the pterygoid plexus, which lies in the infra-temporal region.

Veins of the Orbit. The veins of the orbit correspond, with the exception of the naso-frontal vein, with the branches of the ophthalmic artery, and they gradually converge, as they pass backwards in the orbit, until they form two main trunks, a superior ophthalmic vein and an inferior ophthalmic vein. The two trunks terminate separately, or by a single stem, in the anterior end of the cavernous sinus, to which they pass through the superior orbital fissure, and between the two heads of the lateral rectus muscle.

The superior ophthalmic vein communicates, at the supero-medial angle of the orbit, with the angular vein, and it receives the naso-frontal vein which accompanies the frontal nerve. The inferior ophthalmic vein communicates, through the inferior orbital fissure, with the pterygoid plexus.

Veins of the Nose.—The veins of the walls of the nasal cavity end partly in the ethmoidal tributaries of the superior ophthalmic vein, partly in the septal affluent of the superior labial and in the lateral nasal veins, both of which are tributaries of the anterior facial vein; but the majority of the veins of the nose, both from the septal and lateral walls, join together to form a spheno-palatine vein which passes through the spheno-palatine foramen and the pterygo-palatine fossa, and terminates in the pterygoid plexus.

Plexus Pterygoideus and the Vena Maxillaris Interna.—The pterygoid plexus of veins lies in the infra-temporal and pterygoid fossæ. It covers the lateral surface of the internal pterygoid muscle, and surrounds the external pterygoid. It receives tributaries which correspond with and accompany the branches of the internal maxillary artery-viz., spheno-palatine, pharyngeal, vein of pterygoid canal, infra-orbital, posterior superior alveolar, descending palatine, buccinator, two or three deep temporal, pterygoid, masseteric, and inferior alveolar veins, and the middle meningeal vein. It communicates, superiorly, with the cavernous sinus through the foramen ovale; anteriorly with the inferior ophthalmic vein through the interior orbital fissure; and between the masseter and the buccinator with the anterior facial vein by the deep facial anastomosing branch. It also communicates posteriorly and medially, on the medial side of the internal pterygoid, with the pharyngeal plexus, and it terminates posteriorly in the internal maxillary vein.

The internal maxillary vein is a short vessel which accompanies the first part of the internal maxillary artery, between the spheno-mandibular ligament and the neck of the mandible. Between the neck of the mandible and the antero-medial surface of the parotid gland it joins the upper part of the posterior facial vein. Occasionally the internal maxillary vein is double, and sometimes it is represented by several channels.

The posterior facial vein is formed, immediately above the zygomatic arch, by the union of the superficial and middle temporal veins. It crosses the zygomatic arch, dips deep to the upper part of the parotid gland, and, whilst lying between the antero-medial surface of the gland and the posterior border of the mandible, it receives the internal maxillary vein or veins. Then it descends, through the substance of the parotid, and, emerging from its lower end at the angle of the mandible, it passes forwards and downwards to unite with the anterior facial vein in the formation of the common facial vein.

Whilst it is in the substance of the parotid it gives off a comparatively large branch, which emerges from the lower and posterior part of the gland and forms one of the two commencing tributaries of the external jugular vein.

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VENOUS SINUSES AND VEINS OF THE CRANIUM AND OF ITS

CONTENTS. The venous channels met with in the cranial walls and cranial cavity are :

(1) The diploic veins, which lie in the spongy tissue between the outer and inner tables of the cranial bones.

(2) The meningeal veins, which accompany the meningeal arteries in the outer layer of the dura mater.

(3) The veins of the brain, which lie between the folds of pia mater and in the subarachnoid space.

(4) The cranial venous sinuses, channels which are situated between the outer and inner layers of the dura mater; they receive the blood from the terminal cerebral veins.

DIPLOIC AND MENINGEAL VEINS. Venæ Diploicæ. - The diploic veins are anastomosing spaces in the spongy tissue of the flat bones of the skull; they are lined with endothelium. The number of efferent vessels which emerge from the diploic spaces is not constant, but usually there are at least four on each side-viz., a frontal, two temporal, anterior and posterior, and an occipital.

The frontal diploic vein is one of the most constant; it drains the anterior part

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of the frontal bone, passes through a small aperture in the upper margin of the supra-orbital notch, and terminates in the supra-orbital vein.

The anterior temporal diploic vein drains the posterior part of the frontal bone and the anterior part of the parietal bone; it pierces the great wing of the sphenoid, and terminates either in the spheno-parietal sinus or in the anterior deep temporal vein.

The posterior temporal diploic vein drains the posterior part of the parietal bone; it runs downwards to the posterior inferior angle of the parietal bone and terminates in the transverse sinus, to which it passes either through a foramen in the inner table of the parietal bone or through the mastoid foramen.

The occipital diploic vein is usually the largest of the series; it drains the occipital bone, and terminates either externally in the occipital vein or internally in the lateral sinus.

Venæ Meningeæ.—The meningeal veins commence in two capillary plexuses, a deep and a superficial

. The deep plexus is a wide-meshed network in the inner layer of the dura mater. Its efferent vessels terminate in the superficial plexus. The superficial plexus lies in the outer layer of the dura mater. It consists of numerous vessels of uniform calibre which frequently anastomose together, and terminate in two sets of efferents; of these, one set ends in the cranial blood sinuses, and the other accompanies the meningeal arteries. The efferent meningeal veins are peculiar, inasmuch as they do not alter much in size as they approach their terminations. They lie external to the arteries in the grooves in the inner wall of the cranium, and are very liable to be torn when the bones are fractured (Wood Jones).

· VEINS OF THE BRAIN.

The veins of the brain include the veins of the cerebrum, of the mid-brain, of the cerebellum, of the pons, and of the medulla oblongata. They do not possess valves.

Venæ Cerebri—The Veins of the Cerebrum.—The cerebral veins are arranged in two groups, (a) the deep and (b) the superficial.

The deep veins issue from the substance of the brain. The superficial veins lie upon its surface in the pia mater and the subarachnoid space. The terminal trunks of both sets pierce the arachnoid membrane and the inner layer of the dura mater, and open into the cranial venous sinuses.

(a) The deep cerebral veins are the chorioid veins, the venæ terminales, the internal cerebral veins, the great cerebral vein (Galen), the vein of the septum pellucidum and the inferior striate veins.

Each chorioid vein is formed by the union of tributaries which issue from the chorioid plexus in the body and inferior horn of a lateral ventricle. It ascends, along the lateral border of the tela chorioidea of the third ventricle (0.T. velum interpositum), and passes forwards, in the lateral border of that fold of pia mater, to the interventricular foramen (Monro), where it receives efferents from the chorioid plexus of the third ventricle, and unites with the vena terminalis to form the internal cerebral vein (Galen).

The vena terminalis (0.T. vein of corpus striatum), on each side, is formed by the union of tributaries which issue from the corpus striatum and from the thalamus. It runs forwards between the thalamus and the caudate nucleus, in a groove in the floor of the lateral ventricle, and, after receiving tributaries from the walls of the anterior horn of the ventricle, and the vein of the septum pellucidum, it terminates at the apex of the tela chorioidea, where it joins the chorioid vein to form the internal cerebral vein (Galen).

Each internal cerebral vein (Galen) commences at the apex of the tela chorioidea, near the interventricular foramen (Monro), by the union of the vena terminalis with the chorioid vein. The two veins run backwards between the layers of the tela, receiving tributaries from the chorioid plexuses of the third ventricle and from the fornix and corpus callosum, and they terminate, beneath the splenium of the corpus callosum, by uniting to form the great cerebral vein (Galen).

The great cerebral vein (Galen) passes backwards and slightly upwards from its origin, and ends in the anterior extremity of the straight sinus. In addition to the two internal cerebral veins, by the union of which it is formed, it receives tributaries from the posterior parts of the gyrus cinguli of each side, from the pineal and quadrigeminate bodies, from the medial and inferior surfaces of the occipital lobes of the brain, and from the upper surface of the cerebellum. It also receives the basal vein of each side (see p. 971).

An inferior striate vein descends, on each side, from the substance of the corpus striatum, and, after passing through the anterior perforated substance, ends in the

genu of the

basal vein (see below), which, as already stated, is a tributary of the great cerebral vein.

(b) The superficial cerebral veins are more numerous and of larger calibre than the cerebral arteries. They lie upon the surface of the cerebrum, drain blood from the cerebral cortex, and they are divisible into two sets, the superior and the inferior.

The superior cerebral veins, twelve or more in number, lie in the pia mater and subarachnoid space on the upper and lateral aspect of the cerebral hemispheres. They run upwards and medially, to the margin of the longitudinal fissure where they receive tributaries from the medial surface of the hemisphere, and they terminate in the superior sagittal sinus or in the lateral lacunar expansions of the sinus. The anterior veins of this set are small and run transversely, but the posterior are large and run obliquely forwards and medially; they are embedded for some distance in the wall of the sinus, and their orifices are directed forwards against the blood stream.

The inferior cerebral veins lie on the lower and lateral aspects of the cerebral hemispheres; they run downwards and medially, and terminate in the sinuses which lie at the base of the skull—viz., the cavernous, the superior petrosal, and the transverse sinuses. One of these veins, the superficial middle cerebral vein (0.T. superficial Sylvian), runs along the posterior horizontal branch and the stem of the lateral fissure (Sylvius) to the cavernous sinus; occasionally it is united by an anastomotic loop, known as the great anastomotic vein (Trolard), with the superior sagittal sinus, and sometimes by the inferior anastomotic vein with the transverse sinus.

The anterior cerebral vein of each side lies in the longitudinal fissure, and accompanies the corresponding anterior cerebral artery; it receives tributaries from the corpus callosum and the gyrus cinguli. Turning downwards, round the

corpus callosum, it reaches the base of the brain, and terminates in the basal vein.

The deep middle vein (O.T. deep Sylvian) lies deeply in the lateral fissure (Sylvius); it anastomoses freely with the superficial middle vein, receives tributaries from the insula and the adjacent opercula, and terminates in the basal vein.

The basal vein commences at the anterior perforated substance; it is formed by the union of the anterior cerebral vein with the deep middle vein and with the inferior striate vein. Passing backwards round the pedunculus cerebri, it terminates in the great cerebral vein (Galen). Its tributaries are derived from the tuber cinereum, the corpus mamillare, the posterior perforated substance, the uncus, the inferior cornu of the lateral ventricle, and the pedunculus cerebri.

Veins of the Mid-brain.-The veins of the mid-brain terminate for the most part either in the great cerebral vein (Galen) or in the basal veins.

Cerebellar Veins. These veins also are divisible into two groups, the superficial and the deep. The former are quite independent of and much more numerous than the arteries. They form two sets, the superior and the inferior.

The superior superficial cerebellar veins terminate in a single median or vermian efferent vessel which is sometimes double, and in several lateral efferents. The superior vermian vein runs anteriorly and ends in the great cerebral vein (Galen). The lateral superior cerebellar veins terminate in the transverse sinuses or in the superior petrosal sinuses.

The inferior superficial cerebellar veins also form a small vermian and numerous lateral efferents; the former runs backwards and joins either the straight sinus or one of the transverse sinuses, and the latter end in the inferior petrosal and occipital sinuses.

The deep cerebellar veins issue from the substance of the cerebellum and terminate in the superficial veins.

Veins of the Pons. The deep veins from the substance of the pons pass forwards to its anterior surface, where they become superficial, and, anastomosing together, form a plexus which is drained by superior and inferior efferent veins. The superior efferent veins join the basal vein ; the inferior efferent veins either unite with the cerebellar veins, or they open into the superior petrosal sinus.

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