xiii.] THE FROG. 181 



lymph contained in the wide lymphatic vessels and in the 

 pleuro-peritoneal cavity of the Frog, into these veins. 



The anterior lymph-hearts are situated close to the trans- 

 verse processes of the third vertebra, below the edge of the 

 scapula; the posterior pair lie one on each side of the uro- 

 style, and their pulsations may be observed by carefully 

 watching the integument in this region in a living Frog. 



The Thymus gland is a small rounded body situated im- 

 mediately behind the suspensorium, in a position corre- 

 sponding to the dorsal ends of the obliterated branchial 

 arches. 



The Thyroid gland appears to be represented by two or 

 more oval bodies, which are found attached to the lingual 

 vessels and between the aortic and pulmo-cutaneous trunks. 



The Adrenal glands are yellow bodies imbedded in the 

 ventral face of the kidney. 



The slit-like glottis of the Frog is formed by the apposi- 

 tion of two longitudinal folds of the mucous membrane of 

 the mouth, each of which contains a cartilage of similar 

 form. These cartilages are the arytenoid cartilages. They 

 are articulated with an annular cartilage (laryngo-tracheat) 

 which supports the wall of the very short chamber which 

 represents the larynx and trachea. When the two folds of 

 the glottis are divaricated, there are seen between them two 

 membranous pouches, the free edges of which meet in the 

 middle line, while anteriorly and posteriorly they pass into 

 the mucous membrane which lines the faces of the longitu- 

 dinal folds. These are the vocal ligaments, and the slit 

 between them is what answers to the glottis in Man. It 

 is by their vibration that the croak of the Frog is produced. 



Laterally the laryngo-tracheal chamber opens into the 



