<luct on each side passing from the outer side of the kidney into 

 the cloaca. ( In the male this serves also as a vas deferens. ) 



Make a diagram of the urino-genital system of your specimen. 



m. Tag your specimen with your name and put it into a jar of 

 preserving fluid until the next exercise. 



III. THE NERVOUS SYSTEM. (Preserved Specimen.) 



a. Cut the skin along the median dorsal line and reflect it. Re- 

 move the muscles from the vertebrae. Open the neural canal by 

 cutting into the membrane just posterior to the skull, and bit by 

 bit, pick off the roof of the brain cavity with strong forceps or 

 scissors. Remove the dorsal part of the vertebral arches in the 

 same way. A delicate pigmented membrane ( pia mater} covers the 

 brain and the spinal cord but may be concealed in the latter 

 region by soft tissue ( coagulation products after death ) that can 

 be washed away with a stream of water from a pipette. 



b. T/ie Brain; if this is not injured in exposing it, note: 



1. RhineiicepJialou or anterior part made up of two olfactory 

 lobes extending anteriorly from a common median part as two 

 cylindrical so-called olfactory nerves to branch inside the nasal 

 chambers. 



2. ProsencepJialon composed of two large masses, the cerebral 

 hemispheres, separated by a median groove. 



3. Tlialameuccplialon, a mass between and posterior to the 

 hemispheres. Upon it is a very small pineal gland and below this 

 a central cavity, the third ventricle, bounded on the sides by 

 masses called optic tlialaini. 



4. MesencepJiaion, a pair of large, rounded, hollow bodies, the 

 optic lobes. 



5. Metencephalon or cerebellum, a small mass extending across 

 the anterior edge of a large triangular cavity, the fourth ventricle. 



6. Myelencephalon or medulla oblonyata, forms the remainder of 

 the brain posteriorly and contains the fourth ventricle covered 

 over by a vascular part of the pia mater. 



c. Spinal Cord or My el on. 



1. Forming the continuation of the medulla oblongata outside 

 the skull it rapidly tapers at about the fifth or sixth vertebra to form 

 a slender filament. On its dorsal surface is a median line, thi> 

 dorsal fissure. 



2. On each side ten spinal nerves arise from the cord. By 

 carefully raising the cord a little, towards the posterior end, and 



61 



