searching with a pocket lens, the nerves are seen to arise each by 

 two roots, one dorsal, one ventral. 



J\Iake a sketch of the central nervous system as thus exposed. 



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

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

 remove the brain (as entire as possible), and part of the spinal 

 cord. Place in a dish of water and stuclv the ventral side with a 



/ 



pocket lens. 



1. Optic chiasm 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 re- 

 moving the brain ) . 



2. Tuber cinereum : a rounded somewhat two-lobed elevation 

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

 bulum, or slender neck bearing a small conical mass, the pituitary 

 body or hypophysis cerebri. 



3. Crura cerebri : the anterior continuation of the medulla as 

 the large nerve mass dorsal to the above parts, extending anter- 

 iorly on each side toward the hemispheres. 



4. 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. 



e. Peripheral Nerves: a. Spinal Trunks, (i) Sciatic ple.vns: 

 A number of large nerves, on each side of the dorsal aorta connected 

 by branches and ending posteriorly in the large sciatic 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 obliquely outward and posteriorly along 

 the wall of the body cavity. (3) Branchial nerve; formed from the 

 union of the 2nd, and 3rd spinal nerves; it goes to the arm. 



b. Raise the dorsal aorta and notice the two slender longitudinal 

 sympathetic trunks passing 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 func- 

 tion, surrounding the spinal nerves where they issue from the spaces 

 between the transverse processes of the vertebrae. 



IV. MUSEUM SPECIMENS. 



Observe in the Museum, south wing, numerous preparations of 



62 



