REMOVAL OF THE BRAIN 117 



becomes continuous with the veins of the nasal fossae, or its 

 branches pass through foramina in the nasal bones and join 

 the angular veins ; (b) two parietal emissary veins, which 

 pass through the parietal foramina and connect the superior 

 sagittal sinus with the occipital veins. (2) Emissary veins 

 connected with the transverse sinuses (a) two mastoid 

 emissary veins, one on each side, pass through the mastoid 

 foramina and connect the sigmoid parts of the transverse 

 sinuses with the posterior auricular veins ; (b) two posterior 

 condyloid veins, one on each side, pass through the condyloid 

 canals and connect the lower ends of the transverse sinuses 

 with the plexuses of veins in the sub-occipital triangles. One 

 or both of the posterior condyloid veins may be absent. (3) 

 Emissary veins connected with the cavernous sinuses (a) a 

 vein which traverses the foramen ovale, or the foramen Vesalii, 

 and connects the cavernous sinus with the plexus of veins 

 around the external pterygoid muscle ; (b) a plexus of veins 

 which passes through the temporal bone with the internal 

 carotid artery, and connects the cavernous sinus with the 

 pharyngeal venous plexus ; (c) in a sense, the ophthalmic 

 vein may be considered an emissary vein, for, although under 

 ordinary circumstances it is a tributary of the sinus, blood can 

 flow through it, in the opposite direction, from the sinus into 

 the orbit, and then along the tributaries which connect the 

 ophthalmic vein with the angular vein, and along the channels 

 which connect the ophthalmic vein, through the inferior 

 orbital fissure, with the veins in the infratemporal region. 



The Arteries of the Cranial Cavity. (i) The vertebral 

 arteries; (2) the internal carotid arteries; (3) the meningeal 

 arteries. 



Arterise Vertebrates. The vertebral arteries, right and 

 left, pierce the spinal dura mater below the foramen magnum, 

 through which they enter the cranium. As each artery passes 

 through the foramen it lies anterior to the highest dentation 

 of the ligamentum denticulatum, and it passes between the 

 hypoglossal and first cervical nerves. It was divided when 

 the hind brain was removed, and its cut extremity lies near 

 its point of entrance into the cranial cavity (Figs. 36, 37). 



Arterise Carotides Internse. Each internal carotid artery 

 enters the cranium at the foramen lacerum, between the apex 

 of the petrous part of the temporal bone and the body of the 

 sphenoid, where it pierces the outer layer of the dura mater. 



