The anatomy of the nervous system, from the standpoint of development and function . he telencephalon and diencephalon with freelyintercommunicating cavities. The mesencephalon is well denned and presentsa sharp bend, the cephalic flexure. The rhombencephalon shows signs of sepa-ration into the metencephalon and myelencephalon and is slightly bent dorsallyat the pontine flexure. Another curvature which develops at the junction of 32 THE NERVOUS SYSTEM the brain and spinal cord is known as the cervical flexure (Fig. 16). Fromthe walls of the prosencephalon there develop outpocketings on either
The anatomy of the nervous system, from the standpoint of development and function . he telencephalon and diencephalon with freelyintercommunicating cavities. The mesencephalon is well denned and presentsa sharp bend, the cephalic flexure. The rhombencephalon shows signs of sepa-ration into the metencephalon and myelencephalon and is slightly bent dorsallyat the pontine flexure. Another curvature which develops at the junction of 32 THE NERVOUS SYSTEM the brain and spinal cord is known as the cervical flexure (Fig. 16). Fromthe walls of the prosencephalon there develop outpocketings on either side,which form the optic cups and which are connected to the brain by the opticstalks. From the cup develops the retina and through the stalk grow thefibers of the optic nerve. These structures are, therefore, genetically parts ofthe brain. The Telencephalon of the Human Embryo.—By the time the embryo hasreached a length of 13 mm. the brain has passed into the stage represented by Mesencephalon RhombencephalonMyelenccphalon Amnion (cut) Mesodermal segment 14 Open neural groove. Prosencephalon Stomodccum Amnion (cut) Yolk sac Bodv stalk Fig. 14.—Human embryo of mm. showing the neural tube partially closed. (Kollmann.) diagrams E, F, G of Fig. 7. The lateral wall of the telencephalon, with thecorpus striatum and olfactory brain or rliinenccphalon, has been evaginated oneither side to form paired structures, the cerebral hemispheres (Fig. 16). Ex-cept for the corpus striatum and rhinencephalon the evaginated wall is relativelythin, develops into the cerebral cortex, and is known as the pallium. Thelateral ventricles within the hemispheres represent portions of the original telen-cephalic cavity and communicate with the third ventricle through the inter- llll Ml K \l. I l BE \M) [TS \ ATIVES 33 ventricular foramina, which at this stage arc relatively large. The laminaterminalis, connecting the two hemispheres in front of the third ventri< le, repre- Dietu ephalon P
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectnervoussystem, bookye
