m-LLETIX 31, l-MTKL. STATES NATIONAL MU8EUM. 



,s of all tlH- tailed orders, and are transient in the 



the caudal regioi 



tails of the larva- of the Salieiitia 



Ki-niainsof tliesaiiieare seen in the 

 segmented dorsal uniscles of the Uro- 

 dela. and the segmented median ven- 

 tral, or pnbosternal muscles of the 

 tailed and tailless orders. Between 

 these median series of muscles extend 

 two layers, which suitport the sides 

 of the body cavity, the external and 

 internal oblique. Jn the Urodela the 

 oxteiiial oblique is divided up at the 

 superior border into separate heads, 

 each of which arises from the extrem- 

 ity of a rib. Between the ribs is a 

 band of narrow longitu linal inus- 

 oU'.s—theintercostal.s— which are par- 

 allel to the doisal muscles. Owing 

 to the modilieation of the skeleton 

 the dor.sU niu.><cles in the Salientia 

 are much nioditied, and form chev- 

 rons with the apex posterior. The 

 limb mu.scles are much like those of 

 higher vertebrata. _ 

 The heart of the IJatrachia pos- 

 sesses three chambers, two auricles and one ventricle, and there is a 

 sinus venosus at tlie entrance of ::he vena ca\ a. The bull)us arteriosus 

 is not uuiscular, and has a longitudinal valve or partial septum, or is 

 completely divided into two in the Proteida. In the Urodela there are 

 four aortic branches on each side, whieh are in the larval state branchial 

 arteries. As many veins return from the branchia' and unite above the 

 heart to form the aorta. In develo])inent to matr.rity the arteries be- 

 come connected with the veins by longitudinal vessels, the tluctxs hotaUi, 

 which complete the ''aorta bows" where the oranchial system disap- 

 pears. The first and last of these arches become subordinate, and 

 the intermediate on each .side function as "aorta roots," who.se union 

 forms the aorta. The carotitl artery is a coritinuation of the (hii'tui^ 

 hotaltl «onnecting the first and .second bows, and the last bow is modi- 

 fied into the imlmonary vein. In the Proteida and Trachystoniata 

 three aorta bows remain on each side, and the branchial arteries and 

 veins jiersist. In the Salientia three aorta bows remain, but the second 

 on each side only form the aoita, the first and last forming the carotitl 

 artery and pulmomiry vein. 



The venous system consists primitively, as in other vertebrata. of 

 two anterior and two posterittr cardinal Aeins, which unite on eacii side 

 into a single transverse vessel, the Diicfus '.'uvieri. which empties into 

 the sinus venosus. Subsequently two otlier pairs of longitudinal veins 



Fir,. 2. Diacrani »*' clinnrtrncranium and oranial 

 nervca of Salamaiidia, from litlow (from Wii 

 der8lie:ni). 



