32 THE FROG CHAP. 



With the scissors extend the incision made in the skin of 

 the belly forwards, in a straight line, to the lower jaw. 

 Holding up the edge of the skin with the forceps, cut through, 

 with a scalpel, the partitions between adjacent lymph- 

 sinuses, so as to separate the whole of the skin of the ventral 

 surface from the muscle ; and, having done so, pin back 

 the flaps, right and left (see Fig. 2). Similar cuts should be 

 made in the skin of the limbs and back. Observe 



The fascia, the muscles of the body-wall, the abdominal 

 and musculo-cutaneous veins, and the position of the hyoid 

 (p. 40), sternum (p. 47), shoulder-girdle, and pubic region of 

 the hip-girdle (pp. 46 and 50). 



The Abdomen and its Contents. Pinch up the muscles 

 on one side of the abdominal vein with the forceps, and 

 make an incision in them by a single snip of the scissors. 

 Then, holding the edge of the wound with the forceps, 

 extend the cut forwards to the shoulder-girdle and back- 

 wards to the pubis. Keep the cut parallel to the abdominal 

 vein, and be careful not to wound the latter. You will 

 find that the incision thus made opens a large body-cavity or 

 caelome, in which a number of structures, the abdominal 

 viscera, are contained. Note that the body-wall consists of 

 three layers : (i) skin, (2) muscles, with their fascia, and 

 (3) peritoneum. 



So far, however, the cavity is not thoroughly opened. Lift 

 up the side of the abdominal wall to which the abdominal 

 vein is attached, and very carefully separate the vein by 

 tearing through, with a needle or the point of a scalpel, the 

 connective-tissue by which it is attached to the inner face 

 of the muscles : or, in order to prevent the possibility of 

 injuring the vein, cut through the muscles of the body-wall 

 longitudinally on the other side of the abdominal vein, so 

 as to leave a narrow strip of muscle attached to it. Then 

 make two cross-cuts, starting from the anterior end of the 

 longitudinal incision, and extending outwards towards the 

 fore-limbs : take care not to injure the musculo-cutaneous 

 veins, and pin back the two flaps into which the soft ab- 

 dominal wall is now divided (Figs. 3 and 4). Next dissect 

 away the muscles covering the shoulder-girdle, so as to 

 expose the bones : identify the bones called coracoid and 

 clavicle (compare a skeleton and Fig. 12). With the strong 

 scissors cut through these bones on either side as near as 

 possible to the shoulder-joint : then lift up the sternum 

 and middle portions of the shoulder-girdle, and carefully 

 dissect them away from the underlying parts. 



