" 



CHAPTER III. 



GENERAL ANATOMY. 



1. The Frog. The skin of the frog is very loosely attached 

 to the underlying parts of the body, being, indeed, separated 

 therefrom by a system of subcutaneous lymph spaces (Fig. 8, Sc. I. s.). 

 If, therefore, a frog which has been killed with chloroform be 

 pinned out under water in a dissecting dish, 1 it is an easy matter 

 to slit open the skin along the whole mid ventral line without 

 injuring the body-wall beneath. Note in doing so the parti- 

 tions between separate lymph spaces. By reflecting the flaps of 

 skin on either side, the whole of the ventral body-wall may thus 

 be displayed. It will be seen to be white, and largely com- 

 posed of fibrous bands of muscle running in various directions. 

 In the throat they run transversely; in the median line of 

 the trunk they are longitudinal; on either side of this line 

 they run downwards (i.e. ventrally) and backwards; in the 

 pectoral region they converge towards the shoulders. In the 

 mid-line of the pectoral region is the elongated sternum, on 

 either side of which may be felt the bony bars of the shoulder 

 girdle. On each reflected flap of skin is a large vein (great 

 cutaneous), the main trunk of which passes under the arm-pit. 

 It carries blood from the skin towards the heart. Through the 

 abdominal muscles there is seen a median vein (anterior abdo- 

 minal). At the posterior end of the body may be felt the hip 

 girdle. 



1 A useful vessel is made of tinned iron about 8 inches square, with sides 

 slightly sloping outwards, and 2 inches high, bound with thick iron wire to give 

 firmness. A thin piece of cork nailed on to a thin sheet of lead should fit loosely 

 into the bottom. 



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