32 THE FROG chap, 



skin with a 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-ctUaneous veins, and the shoulder-girdle and pubic region of the 

 hif-girdle. 



The Abdomen and its Contents.— Knch 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 backwards 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 ccelome, 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 i\iAx fascia, and 

 (3) peritonerwi. 



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

 of Ihe 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 longitu- 

 dinally 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 abdominal 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 both these bones as near as possible to the 

 shoulder-joint : then lift up the middle portion of the shoulder-girdle 

 thus separated, and carefully dissect it away from the underlying parts. 



Having thus exposed the whole of the abdominal cavity, pour just 

 enough water into the dissectingidish to cover the animal, first washing 

 away any blood which may have escaped from cut vessels. If your 

 specimen is a female, dissolve a httle common salt in the proportion of 



