THE SPECIAL ANATOMY OF THE FROG 41 



which also opens into the cloaca. Trace it to the cloaca and note that the ureter 

 is closely applied to the dorsal side of the oviduct. 



Draw the male urinogenital system showing all of the above-mentioned parts. 



2. Female urinogenital system. The relations of kidney and ureter are the 

 same as in the male. The ovary, however, bears no relation to the kidney. 

 It and its mesentery have already been noted. The oviducts are a pair of con- 

 voluted tubes, extending the whole length of the body cavity. Trace one 

 anteriorly to the anterior wall of the coelome, where it opens into the body 

 cavity by a funnel-shaped mouth, or ostium, near the base of the lung. Have the 

 assistant demonstrate the ostium to you. Trace the oviduct posteriorly to the 

 cloaca. It widens into a large, thin-walled sac, the uterus, which lies behind 

 (dorsal to) the peritoneum in the cisterna magna. Cut open the cloaca, and 

 locate in its dorsal wall the two openings of the oviducts, situated upon pro- 

 jecting papillae and in the ventral wall, the opening of the urinary bladder. 



Draw the female urinogenital system with the cloaca cut open, showing all 

 parts. 



C. THE RESPIRATORY SYSTEM 



At their anterior ends the two lungs open into a chamber, the larynx, which 

 communicates with the pharynx through the slitlike glottis. The larynx lies 

 just in front of the heart. Consult Holmes, chapter viii, pp. 165-68. Dissect 

 away all the muscles from the under surface of the lower jaw so as to expose the 

 flat body of the hyoid cartilage. Find the two thyroid processes of the hyoid 

 which extend posteriorly and inclose the laryngeal chamber between them. The 

 walls of this chamber are supported by a complicated arrangement of cartilages 

 for which Holmes, Fig. 45 (p. 166), should be consulted. Dissect posteriorly 

 from the larynx and remove or cut through blood vessels or other structures 

 until you have exposed the connection of the lungs with the larynx. Make a 

 longitudinal slit through the ventral wall of the larynx, spread the slides apart 

 and look within for the weal cords, a pair of folds extending lengthwise in the 

 chamber. Find the openings of the, lungs into the latero-posterior walls of the 

 larynx, insert one blade of a scissors into one of the openings and slit open the 

 wall of the lung. Note that the inner wall of the lung is raised up into a network 

 of ridges, which divide the wall into a large number of small chambers or alveoli. 

 Blood vessels run along the ridges and break up into an intricate network of 

 capillaries in the walls of each alveolus, which serves as an air sac. 



Draw the dissection. 



D. THE CIRCULATORY SYSTEM: THE VENOUS SYSTEM 



For this purpose a fresh frog, probably injected, will be supplied. Open it 

 up in the usual way to the left of the median line, but be very careful not to cut 

 any blood vessels, especially near the heart. Be very cautious in spreading the 



