and tympanic cavity. The second bristle appears in the Eustachian 

 recess at the side of the posterior part of the mouth. In the male 

 a small opening anterior to this recess leads into the bnccal sac 

 which can be distended, by means of a small blow-pipe. Turn the 

 fleshy tongue forward and notice its mode of attachment. Note the 

 slit of the glottis and the posterior opening of the mouth into the 

 oesophagus; pass a bristle into the former and a large probe into 

 the latter. There are thus two median and six paired openings, 

 from the mouth cavity in the male frog. Note the small teeth. 



b. The trunk. 



This tapers towards the posterior end where the cloaca! aperture 

 is seen near the dorsal surface. Beneath the skin the hard endoskele- 

 ton can be felt on the dorsal side and on the anterior part of the 

 ventral side. 



c. The limbs. 



1. The anterior pair divided each into three regions, brae Ji him, 

 antebrachium, nianus; the latter with four digits, the innermost of 

 which bears a swollen cushion in the male. 



2. The much longer posterior pair each divided into three re- 

 gions, femur, cms, pes, the latter with five long digits connected 

 by a web. There is a large firm prominence on the inner side of the 

 ankle; callosities are found under the joints of both pes and mauus. 



II. INTERNAL CHARACTERS. 



a. Place the frog under a bell-jar with a sponge saturated with 

 chloroform ; when dead pin out under water on its back. 



b. Cut through the skin along the median ventral line from the 

 posterior end to the jaw (raising the skin from the body and not 

 cutting deep ) ; cut transversely at each end of first cut and turn 

 aside the two large flaps thus made. 



c. On the flap of skin on each side is seen a large vein near 

 the shoulder, the musculo-cutaneous vein. The muscular walls of 

 the abdomen are covered by a thin, shining connective tissue sheath, 

 apoiieurosis, through which in the median region is seen the racJiis 

 abdominis passing from the pelvis to the sternum and somewhat 

 divided by transverse lines into segments or mvotomes. Through 

 this muscle is seen the dark blood of the anterior abdominal vein 

 on the median line. 



d. With a pair of forceps raise the body wall and carefully cut 

 it through by a slit to the right of the median line ; continue this 

 cut from pelvis to sternum and make transverse cuts as in the 



58 



