88o HUMAN ANATOMY. 



Anastomoses of the Ophthalmic Veins. — The ophthalmic veins are throughout destitute 

 of valves and open posteriorly into the cavernous sinus, and, since they also communicate with 

 peripheral veins, they may well be regarded as emissary channels through which the blood may 

 flow either from the cavernous sinus to the peripheral veins or in the reverse direction, as may 

 be determined by the relative pressure within and without the cranium. The principal connec- 

 tions which the veins make are ( i ) with the facial vein, which is itself practically devoid of 

 valves, through their branches of origin ; ( 2 ) with the veins of the nasal cavity through the eth- 

 moidal branches ; and ( 3 ) with the pterygoid plexus by means of a branch of the inferior ophthal- 

 mic which passes downward through the spheno-maxillary fissure. 



Practical Considerations. — The communication between the superior 

 ophthahiiic vein — the largest channel in the adult between the vessels of the venous 

 system of the head and face and the sinuses of the dura mater — and the facial vein, 

 while adding to the danger of intracranial complications as a result of infectious disease 

 situated upon the face (page 873), affords relief to intraocular tension in cases of 

 pressure upon the cavernous sinus, as from an inflammatory exudate or an intra- 

 orbital or intracranial growth. Such relief delays the appearance of ' ' choked disc' ' 

 (page 1471), due to the distension of the tributaries of the vein, especially the poste- 

 rior ciliary veins and the vena centralis retinae. In arterio- venous aneurism of the 

 cavernous sinus and internal carotid artery — due to basal cranial fracture, a buUet- 

 or stab-wound, or to idiopathic vascular degeneration — the ophthalmic veins are 

 usually compressed and may transmit pulsation from the sinus to the dilated veins 

 of the eyelids and of the frontal region. The conjunctivze are congested. Exoph- 

 thalmos (page 1439). bruit and thrill are not uncommonly present as a result of 

 involvement of the intraorbital veins. Nervous symptoms — noise in the head, 

 intracranial or frontal pain and paralyses — are rarely absent. 



These symptoms may be simulated by those caused by traumatic aneurism of 

 an orbital artery or by the direct pressure of an internal carotid aneurism on the 

 ophthalmic vein as it empties into the sinus. 



The External Jugular Vein. 



The external jugular vein (v. jugularis externa) (Fig. 759), notwithstanding its 

 usual connection with the subclavian, is closely related both in its development and 

 topographical relations with the internal jugular, and may be most conveniently con- 

 sidered here. It is formed in the neighborhood of the angle of the mandible by the 

 union of the temporo-maxillary and posterior auricular veins, and couises downward 

 immediately below the platysma, crossing the sterno-cleido-mastoid muscle obliquely. 

 In the lower part of the neck it pierces the superficial layer of the deep cervical 

 fascia, sometimes above and sometimes below the posterior belly of the omo-hyoid, 

 and opens into the subclavian vein near its junction with the internal jugular. A 

 short distance below its origin it gives ofi a large branch which passes forward and 

 downward to communicate with the facial vein. 



At its entrance into the subclavian it is provided with a pair of valves, and usually 

 a second pair occurs at about the middle of the neck. A third pair is occasionally 

 present in the interval between the other two. and all of them are insufficient. 

 The superficial layer of the deep* cervical fascia is intimately adherent to the walls 

 of the vein at the point where the latter perforates it, and sometimes the fascia 

 is especially thickened immediately below and to the inner side of the vein. This 

 attachment of the fascia prevents any collapse of the walls of the lower part of the 

 vein, if for any reason there is a deficiency in the amount of blood it contains, and 

 predisposes, therefore, to the entrance of air in case the vein is severed. 



Variations. — Considerable differences of opinion exist as to the definition of the external 

 jugular vein. Some authors describe it as formed by the union of the posterior auricular and 

 occipital veins, the communicating branch described above as occurring between it and the 

 facial being then regarded as the main stem of the temporo-maxillary ; others, again, regard it 

 as formed by the union of the temporal and maxillary veins, the temporo-maxillary then con- 

 stituting its upper portion. 



The vein is subject to considerable variation in size, an inverse correlation existing between 

 it and the anterior jugular. It may even be entirely wanting or, on the other hand, it may be 

 double throughout a portion of its course. It occasionally divides below, one branch passing, 

 as usual, to the subclavian, while the other, passing over the clavicular attachment of the sterno- 

 cleido-mastoid, opens into either the anterior or the internal jugular. 



