no. 3607 KINESIS OF AVIAN SKULL — ZUSI 5 



and then anaesthetized by intramuscular injection of equitheesin 

 (0.20 ml. per 100 grams body weight, or more if necessary). Great 

 care was taken to ensure that the birds were anaesthetized completely 

 before and during the experimentation. Feathers of the head and 

 neck were trimmed and the skin of both sides of the head reflected 

 as soon as the bird lost consciousness. After the head support was 

 fastened firmly to the bird, the support was held motionless by a 

 vise and the body of the bird supported by the table or horizontally 

 suspended in a plastic tube (fig. 3). The exposed jaw muscles were 

 kept moist and clean throughout the experiments by periodic flushing 

 with avian Ringer's solution at 38° C. The depressor mandibulae 

 muscles were caused to contract simultaneously by a tetanizing 



clomp 



head 

 support 



electrode 

 stimulator 



Figure 3. — Diagram of experimental setup for stimulating the depressor mandibulae 

 muscles. The bill was photographed as viewed in the diagram before and during muscle 

 stimulation. 



stimulus of 20 volts (using two Harvard apparatus stimulators) 

 applied through electrodes. The tips of both copper wires of each 

 electrode were fitted with platinum wire bent as a triangle with one 

 point of the triangle soldered to the wire and the opposite side of 

 the triangle placed against the surface of the muscle. The bases 

 of the two triangles of each electrode were parallel, about three mm 

 apart, and were placed perpendicular to the long axis of the muscle. 

 This type of contact gave consistent contractions, was easily applied 

 and adjusted, and caused no damage to the muscles. Before stimu- 

 lating the muscles simultaneously, each was individually stimulated 

 to see that both were performing in a similar manner. Only at 

 voltages exceeding 50 (and especially approaching 100) were there 



