730 THE VASCULAR SYSTEMS 



The transverse or basilar sinus (plexus basilaris) (Figs. 507 and 508) con- 

 sists of several interlacing veins between the layers of the dura over the basilar 

 process of the occipital bone, which serve to connect the two inferior petrosal 

 sinuses. They communicate with the anterior spinal veins. 



The emissary veins (emissaria) are vessels which pass through apertures in 

 the cranial wall and establish communications between the sinuses inside the 

 skull and the diploic veins in the diploe, and the veins external to the skull. 

 Some of these are always present, others only occasionally so. They vary 

 much in size in different individuals. The principal emissary veins are the 

 following: (1) A vein (emissarium mastoideum) almost always present, runs 

 through the mastoid foramen and connects the lateral sinus with the posterior 

 auricular or with the occipital vein. (2). A vein (emissarium parietale) which 

 passes through the parietal foramen and connects the superior sagittal sinus with 

 the veins of the scalp. (3) A plexus of minute veins (rete canalis hypoglossi), 

 which pass through the anterior condylar (hypoglossal) foramen and connect 

 the occipital sinus with the vertebral vein and deep veins of the neck. (4) An 

 inconstant vein (emissarium condyloideum) which passes through the posterior 

 condylar foramen and connects the lateral sinus with the deep veins of the neck. 

 (5) A plexus of veins (rete foraminis ovalis] connects the cavernous sinus with 

 the pterygoid and pharyngeal plexuses through the foramen ovale. (6) Two 

 or three small veins run through the foramen lacerum medium and connect the 

 cavernous sinus with the pterygoid arid pharyngeal plexuses. (7) There is some- 

 times a small vein connecting the same parts and passing through the inconstant 

 foramen of Vesalius opposite the root of the pterygoid process of the sphenoid 

 bone. (8) A plexus of veins (plexus venosus caroticus internus) traverses the 

 carotid canal and connects the cavernous sinus with the internal jugular vein. (9) 

 A small vein (emissarium occipitale) usually connects the occipital vein with 

 the lateral sinus or the torcular Herophili and the occipital diploic vein. (10) A 

 vein is usually transmitted through the foramen cecum and connects the superior 

 sagittal sinus with the veins of the mucous membrane of the nose. 



Applied Anatomy. These emissary veins are of great importance in surgery. In addition 

 to them there are, however, other communications between the intra- and extracranial circula- 

 tion, as, for instance, the communication of the angular and supraorbital veins with the ophthal- 

 mic vein at the inner angle of the orbit, and the communication of the veins of the scalp with 

 the diploic veins. Through these communications inflammatory processes commencing on the 

 outside of the skull may travel inward, leading to osteophlebitis of the diploe and inflammation 

 of the membranes of the brain. To this in former days was to be attributed one of the principal 

 dangers of scalp wounds and other injuries of the scalp. 



By means of these emissary veins blood may be abstracted almost directly from the intra- 

 cranial circulation. For instance, leeches applied behind the ear abstract blood almost directly 

 from the lateral sinus by means of the vein passing through the mastoid foramen. Again, epigj- 

 taxis in children will frequently relieve severe headache, the blood which flows from the nose 

 being derived from the .superior .s;i<riital sinus by means of the vein which passes through the 

 foramen cecum. 



VEINS OF THE UPPER EXTREMITY AND THORAX. 



The veins of the upper extremity are divided into two sets, superficial and deep. 



The Superficial Veins are placed immediately beneath the integument between 

 the layers of the superficial fascia. 



The Deep Veins accompany the arteries, and constitute the venae comites of 

 those vessels. 



Both sets of vessels are provided with valves, which are more numerous in the 

 deep than in the superficial veins. 



