THE FROG 21 



IV. THE CCELOMIC CAVITY. 



The work of this section should be done on a freshly- 

 killed specimen. The method of cutting the frog open will 

 be demonstrated at each table, but each student should per- 

 form the operation on his own specimen. The inflation of 

 the lungs and the bladder will be demonstrated. 



A. Preliminary Dissection. Place the frog on its back, 

 with the head pointing away from you, and with the smaller 

 pair of scissors divide the skin in the ventral median line 

 from the posterior to the anterior end of the body. 



How and where on the ventral surface is the skin at- 

 tached? Observe the great lymph spaces or sinuses be- 

 neath the skin, between the attachments. Turn the flaps of 

 skin outward and pin them to the tray; to do this it will be 

 necessary to sever certain of the attachments. 



Note (by feeling) the cross-shaped pectoral girdle, the 

 center of which lies in the line uniting the bases of the two 

 arms (examine the pectoral girdle in a preparation of the 

 skeleton of the frog). The longitudinal bar of the cross is 

 the sternum. 



Make a longitudinal incision through the ventral body- 

 wall, a little to the left of the median line and extending 

 from the posterior end of the body to the hinder end of th< 

 sternum; be careful not to cut the vein running along the 

 median line. Be careful also not to injure the bladder (de- 

 scribed below). Observe the anterior abdominal vein in 

 the middle line on the under surface of the larger flap. 



With your stronger pair of scissors carry the incision for- 

 ward through the pectoral girdle to the level of a line join- 

 ing the angles of the jaws. 



