288 THE HUMAN BODY. 



it joins the anterior root to make up the common nerve- 

 trunk. Immediately after its formation by the mixture of 

 fibres from both roots, the trunk begins to divide into 

 branches for the supply of some region of the body. 



The Brain (Fig. 82) is far larger than the spinal cord 

 and more complex in structure. It weighs on the average 

 about 50 ounces in the adult. The brain consists of three 

 main masses, each with subsidiary parts, following one an- 

 other in series from before back, and respectively known 

 as the fore-brain, mid-brain, and hind-brain. In man 

 the fore-brain, A, weighing about 44 ounces, is much 

 larger than all the rest put together and laps over them. 



FIG. 82. Diagram illustrating the general relationships of the parts of the 

 brain. A, fore-brain; 6, mid-brain; B, cerebellum; C, pons Varolii ; D, medulla 

 oblongata; B, C, and D together constitute the hind-brain. 



What becomes of the common trunk formed by the mixture of 

 the roots? 



Point out characters in which the brain differs from the spinal 

 cord. What is its weight? Of what main divisions is the brain 

 composed? Which is the largest division? Its weight? 



