NERVOUS SYSTEM AND SENSE ORGANS 31 



Remove the muscles jrom the hack of the head. Bend the 

 head ventrally until a space is formed between the skull 

 and the vertebral column. It exposes a dark membrane. 

 Remove this with forceps and the white brain will be seen 

 beneath it. Make two longitudinal cuts with scissors 

 through the dorsal surface of the skull, taking great care 

 to cut upward so as not to injure the brain. Slowly whittle 

 away the skull roof until the brain is exposed. Do not 

 attempt to remove it at this time. Identify the following 

 parts from the dorsal side. 



172. The olfactory lobes (rhinencephalon) are at the 

 level of the caudal margins of the eyes. They give 

 off the olfactory (first cranial) nerves (181) from 

 their cephalic ends. 



173. The cerebral hemispheres (telencephalon) are 

 separated from the olfactory lobes by a shallow 

 groove. They are separated from each other by a 

 sagittal fissure. 



174. The diencephalon lies caudal and a little ventral to 

 the telencephalon. At its anterior end is a small 

 cavity, covered, in life, by the anterior chorioid 

 plexus which may not appear in a preserved speci- 

 men. Behind this, in exceptionally good dissections, 

 may be seen 



175. a small, dark, vascular body, the paraphysis, and 



176. a thin, small tube, the epiphysis (5). 



177. Caudal to the diencephalon and rising dorsally, are 

 the optic lobes (mesencephalon). 



178. Caudal to this and at a more ventral level, is a small 

 transverse fold, the cerebellum (metencephalon). 



179. The most caudal division of the brain is the medulla 

 oblongata (myelencephalon), which narrows at its 

 caudal end to join the spinal cord (180). Its roof 



