32 THE FROG chap. 



skin with a forceps, cut tVirough, with a scalpel, the partitions between 

 adjacent lymph-sinuses, so as to separate the whole of the skni 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 fasn',-1, the muscles of the body-wall, the abdominal and 

 miisciilo-cutancous veins, and the shoiMtr-girdlc and pubic region of the 

 Jiip-girdle. 



The Abdomen and its Contents.— i'inch 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. "V'ou will find that the incision 

 thus made opens a large body-cavily or ccclome, 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 ^^itvc fascia, and 

 (3) penloneni}!. 



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

 of the abdominal wall t'j which the abdominal vein is attached, and 

 ver)' 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 i>f the abdc^minal 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 f'-re-limbs ; take care not to injure the musculo-cutaneous 

 veins, and pin back the twn flaps into which the soft abdominal wall is 

 niiw divided (Figs. 3 and 4). Next dissect away the muscles covering 

 the shoulder-girdle, so as to expose the bones : identify the bones 

 calk/d coracoid and clavicle (compare a skeleton and Fig. 12). With 

 the strong scissors cut througli botlr 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 dissecting-dish to cover the animal, first washing 

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

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



