GENERAL BIOLOGY 



e. REMOVAL OF CENTRAL NERVOUS SYSTEM. 



1. Cut the olfactory nerves away from the skull, gently turn 

 the brain back cutting all the nerves close to the skull and thus 

 remove as entire as possible the brain and spinal cord. Place in 

 a dish of water and study the ventral side with a pocket lens. 



2. Optic cJiiasm or commissure, a transverse elevation at the 

 posterior end of the cerebral hemispheres continued up on the 

 sides of the brain towards the optic lobes as the optic tracts, and 

 giving rise in the other direction to the optic nerves, (cut off in 

 removing the brain). 



3. Tuber cinereum, a rounded somewhat two-lobed elevation 

 posterior to the chiasm, continued ventrally into the conical in- 

 fundibulum, which bears at its lower end a small conical mass, 

 the pituitary body or hypophysis cerebri. 



4. Crura cerebri, the large nerve bundles, extending anteriorly 

 on each side from the medulla toward the cerebral hemispheres. 



5. Ventral fissure, a median longitudinal groove along the ven- 

 tral side of the medulla and spinal cord. 



Draw the ventral surface of the brain and spinal cord. 



f. PERIPHERAL NERVES. 



a. Spinal Trunks. In the dorsal wall of the body cavity ob- 

 serve : 



(i) Sciatic plexus: A number of large nerves, on each side of 

 the dorsal aorta, connected by branches and ending posteriorly in 

 the sciatic (leg) nerve, while anteriorly it is formed from the 

 7th, 8th, and 9th spinal nerves. (2) Anterior to the sciatic plexus, 

 three pairs of small spinal nerves, the 6th, 5th, and 4th pass ob- 

 liquely outward and posteriorly along the wall of the body cavity. 

 (3) Brachial plexus, formed from the union of the 2nd and 3rd 

 spinal nerves ; it goes to the arm. 



b. Sympathetic System. 



Raise the dorsal "aorta and notice the two slender longitudinal 

 sympathetic trunks dorsal to it, one on each side. ( i ) Each trunk 

 has numerous enlargements or ganglia giving off fine nerves. (2) 

 Large lateral trunks connect these ganglia with the spinal nerves. 

 (3) Periganglionic glands; white masses of unknown function, 

 surrounding the spinal nerves where they issue from the spaces 

 between the transverse processes of the vertebrae. 



Draw these peripheral nerves. 



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