MsS 



A MANUAL OF ANATOMY 



Blood-supply of the Choroid Plexuses. — The choroid plexus ol the lateral 

 ventricle derives its blood from (i) the anterior choroidal artery, which is a 

 branch of the internal carotid ; and (2) the posterior choroidal arteries, which 

 are branches of the posterior cerebral. The choroid plexuses of the third 

 ventricle derive their blood from the posterior choroidal arteries. The 

 choroid plexuses of the fourth ventricle derive their blood from the posterior 

 inferior cerebellar arteries. 



The velum interpositum derives its blood from the posterior choroidal arteries 

 and from the superior cerebellar eirteries. 



Lymphatics of the Brain. — There are no lymphatic vessels in the brain. 

 Their place is taken by spaces in the outer coat of the arteries, called peri- 

 vascular spaces, which are in communication with the subarachnoid space. 



Development of the Encephalon. 



The encephalon is developed from the cephalic part of the neural tube. 

 This part of. the tube undergoes enlargement, and is divided by constrictions 

 into three parts, called the anterior, middle, and posterior primary cerebral 

 vesicles. The anterior primary cerebral vesicle forms the prosencephalon or 



Fig. 



610. — Brain of an Embryo about Three and a Half Weeks Old. 

 From Quain's 'Anatomy' (His). 



Telencephalon 

 Thalamencephalon 

 Mesencephalon 

 Metencephaloii 



5. Myelencephalon 



6. Cervical Flexure 



7. Spinal Cord 

 Pontine Flexure 



9 Olfactory Lobe 

 t, 2 = Prosencephalon ; 3 = Mesencephalon ; 4, 5 = Rhombencephalon 



fore-brain ; the middle primary cerebral vesicle constitutes the mesencephalon 

 or mid-brain ; and the posterior primary cerebral vesicle gives rise to the 

 hind-brain, or rhombencephalon (rhomb-brain, from the rhomboid character 

 of the floor of the fourth ventricle). The constriction between the mesen- 

 cephalon and rhombencephalon is called the isthmus. It gives rise to the 

 valve of Vieussens. 



From the lower part of each lateral wall of the anterior primary cerebral 

 vesicle (telencephalon) a hollow protrusion is developed. These two protru- 

 sions constitute the optic vesicles. 



Flexures of the Primitive Encephalon. — Prior to the subdivision of the three 

 primary cerebral vesicles three flexures make their appearance, called cephalic 



