148 AMPHIBIA (the frog) 



(c) How many bones enter into the articulation at the 

 shoulder-joint? 

 (6) The Pelvic Girdle. Notice the two long bones (iha) 

 one on either side of the urostjde. 



(a) To what is the anterior end attached? 



(b) What makes the "hump" on the frog's back? Of 



what use is this arrangement? 



(c) At the posterior end of the urostyle notice a wedge 



or disk-shaped body, partly bone and partly 

 cartilage. This disk is formed by the union of the 

 posterior extremities of the ilia and the fusing 

 together of the two pubes and the two ischia. 



(d) For what bones do they form sockets (acetabula)? 



Are these acetabula far apart or very close to- 

 gether? Why? 



(e) How close are the articulations of the thigh bone to 



the posterior end of the body? Why? 



(f) Mount this skeleton on a heavy card or a nicely 



planed pine board and save it for further refer- 

 ence in the systematic studies. 

 6. The Nervous System. If it is desired to work out the 

 nervous system, chloroform the specimen, slit open the abdomen 

 and the skin along the dorsal side, and put it into 70 per cent, 

 alcohol, or 2 to 4 per cent, formalin for about a week, then dis- 

 sect out the nervous system. 



(1) Carefully remove the muscles and bones from the 



dorsal surface of the cranium and backbone with 

 knife, bone-forceps, or strong forceps, bit by bit, 

 until the brain and spinal cord are exposed, but left 

 intact. Man's brain has three coverings: dura 

 mater, pia mater, and arachnoid. Can you identif}^ 

 these coverings on the frog's brain and spinal cord? 



(2) The Brain.i 



(a) The Cerebrum. Identify it with its two hemispheres 

 between the eves. 



(1) Shape? 



(2) Size? 



(3) Is it convoluted or smooth? 



(4) Function? 



^See Fig. 185, "Principles of Economic Zoology." 



