VEINS OF THE DIPLOE. 337 



verse inosculation ; but sometimes the vein is single and bifurcates at the 

 root of the nose, into the two angular veins. From the nasal arch, the 

 frontal is continued downwards by the side of the root of the nose, under 

 the name of the angular vein ; it then passes beneath the zygomatic mus- 

 cles and becomes the facial vein, and descends along the anterior border 

 of the masseter muscle, crossing the body of the lower jaw, by the side of 

 the facial artery, to the submaxillary gland, and from thence to the inter- 

 nal jugular vein in which it terminates. 



The branches which the facial vein receives in its course are, the supra- 

 orbital, which joins the frontal vein ; the dorsal veins of the nose which 

 terminate in the nasal arch ; the ophthalmic, which communicates with 

 the angular vein ; the palpebral and nasal, which open into the angular 

 vein ; a considerable trunk, the alveolar, which returns the blood from the 

 spheno-maxillary fossa, from the infra-orbital, palatine, vidian, and spheno- 

 palatine veins, and joins the facial beneath the zygomatic process of the 

 superior maxillary bone, and the veins corresponding with the branches 

 of the facial artery. 



The Internal maxillary vein receives the branches from the zygomatic 

 and pterygoid fossae ; these are so numerous and communicate so freely as 

 to constitute a pterygoid plexus. Passing backwards behind the neck of 

 the lower jaw r , the internal maxillary joins with the temporal vein, and the 

 common trunk resulting from this union constitutes the temporo-maxillary 

 vein. 



The Temporal vein commences on the vertex of the head by a plexiform 

 network which is continuous with the frontal, the temporal, auricular, and 

 occipital veins. The ramifications of this plexus form an anterior and a pos- 

 terior branch which unite immediately above the zygoma ; the trunk is here 

 joined by another large vein, the middle temporal, which collects the blood 

 from the temporal muscle, and around the outer segment of the orbit, and 

 pierces the temporal fascia near the root of the zygoma. The temporal 

 vein then descends between the meatus auditorius externus and the con- 

 dyle of the lower jaw, and unites with the internal maxillary vein, to form 

 the temporo-maxillary. 



The Temporo-maxillary vein formed by the union of the temporal and 

 internal maxillary, passes downwards in the substance of the parotid gland 

 to its lower border, where it becomes the external jugular vein. It receives 

 in its course the anterior auricular, masseteric, transverse facial, and paro- 

 tid veins, and near its termination is joined by the posterior auricular vein. 



The Posterior auricular vein communicates with the plexus upon the 

 vertex of the head, and descends behind the ear to the temporo-maxiU'ary 

 vein, immediately before that vessel merges in the external jugular. It 

 receives in its 'course the veins from the external ear and the stylo-ma'Stoid 

 vein. f 



The Occipital vein commencing posteriorly in the plexus of the vertex 

 of the head, follows the direction of the occipital artery, and passing deeply 

 beneath the muscles of the back part of the neck, terminates in the internal 

 jugular vein. This vein communicates with the lateral sinus by means of 

 a large branch which passes through the mastoid foramen, the mastoid vein. 



VEINS OF THE DIPLOE. 



The diploe of the bones of the head is furnished in the adult with irregu- 

 lar sinuses, which are formed by a continuation of the internal coat of tht 

 29 w 



