26 THE FROG chap. 



These are the kidneys. With the outer edge of each is 

 connected a tube, the ureter (iir), by which the urine, 

 formed in the kidneys, is carried to the cloaca (Fig. 7). 



It has been pointed out that the abdomen is Hned 

 by peritoneum, and that the various organs are suspended 

 by folds of the same membrane, called, in the case of the 

 enteric canal, the mesentery. The relations of this mem- 

 brane are best seen in a diagrammatic transverse section of 



cC.ao 1 / •'^ S.CIL.C1/.S 



v.Jb^r' 



czhd.v 



Fig. 5. — Diagrammatic transverse section through the trunk of a frog, to show the 

 relations of the peritoneum. 

 abd. V. abdominal vein ; d. aa. dorsal aorta ; ii. ilium ; int. intestine ; kd. 

 kidney ; tn. muscles of back ; nz". muscles of abdomen ; vtes. mesentery ; p, per. 

 parietal layer of peritoneum ; p.per^. the same, turning down to cover the 

 kidney ; pt. cv. postcaval vein ; sk. skin ; s. cu. ly. s. sub-cutaneous lymph- 

 sinu.'^es ; spy. spermary ; s. v. ly. s. sub-vertebral lymph sinus ; u. st. urostyle 

 (part of the vertebral column); v. per. visceral layer of peritoneum, investing in- 

 testine ; "u. per' , the same, investing spermarj-. 



the body (Fig. 5), though many points can be perfectly 

 well made out from the actual specimen. The body-cavity 

 is lined by what is called the parietal layer of the 

 peritoneum (/. per\ which adheres closely except in the 

 middle dorsal region, where it leaves the body-wall and 

 becomes closely apphed to the ventral surface of the 



