88 STUDIES OP ANIMAL LIFE. 



(5) The medulla, the wedge-shaped posterior por- 

 tion of tlie brain. 

 b. The depression seen in the medulla is a portion 

 of the cavity of the hollow brain revealed by 

 the cutting away of the very thin dorsal wall 

 of this region. 



3. The Spinal Cord. 



a. What is its shape? 



b. How far does it extend posteriori}' ? 



c. Identify in a prepared cross-section, — 



(1) the dorsal and ventral grooves ; 



(2) the central cavity ; 



(3) the two roots of a spinal nerve, on each side 



of the cord near the grooves ; 



(4) the "gray matter " in the form of a letter H ; 



(5) the "white matter" surrounding the gray 



matter. 



4. Draw the brain and spinal cord from the dorsal 



view. 



5. Make a diagram of a cross-section of the spinal cord. 



N. The Skeleton. 



1. Observe the division of the skeleton into two prin- 



cipal groups of bones : — 



a. The axial skeleton, consisting of the bones of 



the head (skull) and the backbone (vertebral 

 column). 



b. The appendicular skeleton, consisting of the bones 



of the limbs and the girdles to which the limbs 

 are attached. 



2. The Skull. 



a. Premaxillaries and maxillaries, the bones of the 

 upper jaw. 



