THE NERVES. 377 



wall of the cranial cavity, between the anterior and middle fossae, 

 uniting with V. meningea media ; it receives the anterior diploica 

 temporal., and opens into the sinus cavernosus (ophthalmicus). 



The vessels and nerves of the dura mater. Arteries : me- 

 ningece anterior., from ethmoidalis * media, from maxillaris in- 

 terna ; poster iares, from pharyngea ascendens, occipitalis and 

 vertebralis. 



Veins : Vv. meningece, double for each artery, open into the 

 sinus and into plexus pterygoideuss Lymphatics are wanting 

 (Arnold) ; those on the internal wall belong to the arachnoidea. 

 Nerves : branches from the first division of trigeminus and troch- 

 learis, two long branches near the middle line. 



2. Arachnoidea (the serous membrane). The external surface 

 of the pia mater is covered with pavement epithelium, which ex- 

 tends over the convolutions of the brain like a bridge, passes upon 

 the internal surface of the dura mater, firmly attached to it by 

 uniting tissue, and thus forms a closed sac, which does not enter 

 the cerebral cavities, lies between pia and dura mater, and con- 

 tains in its cavity, even during life, a serous fluid (fluidum cere- 

 bro-spinale) which may be pressed out in drops, or in a jet, after 

 piercing it. 



3. Pia mater s. meninx vasculosa, the soft, vascular envelope, 

 a thin membrane formed of a vascular rele, and uniting tissue, 

 lies close upon the surface of the brain, surrounded by the internal 

 layer of the arachnoidea; enters the sulci and ventricles, and 

 forms 



The plexus choroidei, which folded in a curly form are situated, 

 one in each ventricle, but continue uninterruptedly into one 

 another, and send numerous blood-vessels into the substance 

 of the brain. They are covered with epithelium, which is 

 distinguishable from the ciliated epithelium of the ventricles. 



626. Vessels of the Brain. 



The brain is largely supplied with blood, the course of which is 

 retarded by the convolutions of the arteries. These quickly ra- 

 mify on the surface, and penetrate thus into the cortical substance : 

 other branches pass into the cavities, form the plexus choroidei, 

 and supply from this point the medullary substance. 



There are the two carotides internee, and vcrtebrales. 



The cerebrum is supplied by branches from both, the cerebellum 

 from those of the vertebral alone; namely : 



a. The cerebrum by : art. corporis callosi and its two Rr. com- 



