296 



ZOOLOGY 



SECT. 



as Siren, Amphiuma, and the Gymnophiona, the laryngo-tracheal 

 chamber is prolonged into a distinct trachea or wind-pipe, supported 

 by cartilages. In many species of Salamanders the lungs are absent, 

 and respiration is exclusively cutaneous and pharyngeal. 



Circulatory Organs. The heart always consists of a sinus 

 venosus, right and left auricles, ventricle, and conus arteriosus. 

 The sinus venosus opens into the right auricle, the pulmonary 

 veins enter the left, and the two are separated by a septum 

 auricularum which forms a complete partition in Anura, but in 

 Urodela and Gymnophiona is more or less fenestrated, i.e. formed 

 of a network of muscular strands with intervening spaces. The 



eacl.ca.r- 



R 



c art 



d.a.o 



FIG. 964. Heart and chief arteries of Salamandra. A. larva ; B, adult, a/, br.a. 1 4, 

 afferent branchial arteries ; 6.00. bulbus aortse ; car.yl. carotid labyrinth ; c. art. conus 

 arteriosus ; (/. a,o. dorsal aorta ; rf. bot. ductus Botalli ; ex. br. 1 <?, external gills ; ext. car. 

 external carotid ; int. car. internal carotid ; /. an. left auricle ; Ing. lung ; pi. plexus, giving 

 rise to carotid labyrinth ; pul. a. pulmonary artery ; r. au. right auricle ; c. ventricle. 

 (Altered from Boas.) 



conus arteriosus has no longitudinal valve in the lower Urodela 

 and the Gymnophiona, but is separated both from the ventricle 

 and from the bulbus aortaB by transverse rows of valves. 



In the perennibranchiate Urodela and in the larvae of the air- 

 breathing forms the circulation is essentially like that of a Fish. 

 The bulbus aortse (Fig. 964, A, b. ao.), which represents an abbre- 

 viated ventral aorta, gives off four afferent branchial arteries (af. 

 br. a. 1 4)) three to the external gills, and a fourth which curves 

 round the gullet and joins the dorsal aorta directly. From 

 each gill an efferent branchial artery brings back the purified blood, 

 and the efferent arteries unite, in a somewhat irregular way, to 

 form the dorsal aorta (d. ao.}. Each afferent with the corresponding 

 efferent artery constitutes an aortic arch. Short connecting branches 

 unite the afferent and efferent arteries of each gill, carotids (ext. 

 car., int. car.) arise from the first efferent artery, and, when the 



