244 BULLETIN 34, UNITED STATES NATIONAL MUSEUM. 



scribed {antea) tliere are four cartilaginous arcbes below the ceruto- 

 braucliials, which belong to the dermal system, and which are called ex- 

 trabranchials. Proximally the first of these is articulated with the an- 

 terior exterior angle of the hyobranchial i)late. Distally the four are 

 united together. These arches support a system of branchial fringes, 

 which are internal in position, and are contradistinguished from the ex- 

 ternal branchiae which the Salientia exhibit when first hatched, and 

 which are the only branchiae of the Urodele and other tailed types. They 

 are thought by Huxley and Parker to be homologous with the branchial 

 structures of the Marsipobranchii or lampreys. (Plate 51, fig. 1.) 



The development of the auditory ossicles and cartilages exhibits the 

 following facts. The epistapedial disk appears in its normal position, 

 covering the flexure of the quadrate cartilage. The interstapedial ap- 

 pears as a bud in front of and distinct from the stapes, and the meso- 

 stapedial appears as a small membrane on its apex. At a period of its 

 growth the interstiii)edial cartilage connects the stapes with the quad- 

 rate cartilage, as in Trematodera and larval Pseudosaurian Urodela. At 

 the same time the ceratohyal articulates with the quadrate more dis- 

 tallj^, so that at this stage a Kana presents the characters of a transi- 

 tional stage seen in the salamandrine genera Spelerpes and Plethodon. 

 The interstapedial then elongates until it reaches the anuulus tymi)ani- 

 cus. These facts go to show that the interstapedial and mesostapedial 

 are not segmented from the ceratohyal or meckeliau arches, and are 

 therefore not homologous with the ossicula auditus of mammalia, unless, 

 indeed, the embryonic record has been greatly falsified by csenogeny. 

 (Plates 49, 50.) 



ORlGrlN AND EVOLUTION OF THE SALIENTIA. 



The oldest Salientia of which we have any knowledge were obtained 

 from the Jurassic beds of the Kocky Mountains by Professor Marsh.* 

 They occur in lower Eocene beds in North America (Green liiver 

 shales)t and in Middle Miocene of Switzerland (Eppelsheim)f and Ger- 

 many (Braunkohle of the Rhine). § They are not rare in the Upper Mio- 

 cene of North America (Loup Fork, of Kansas). || Forms which by their 

 structure would connect this order directly with the extinct orders 

 are unknown. It is, however, entirely probable that, as already pointed 

 out (p. 14), the Salientia were derived from the Rhachitomi, but whether 

 the Stegocephali enter the line or not is uncertain. The compacted in- 

 ferior i)elvic elements without obturator foramen of the Salientia is much 

 like the same condition in the Rhachitomi, and to produce an almost 



* Proceed. British Ac. Sci., 1887, Abei'deou ; ou the evidence furnished by Dr. Otto 

 Meyer. 



tCope, Kept. U. S. Geol. Snrv. Terrs., in, 1885, p. 100. 



jTschudi, Classif. d. Batrachier, 1838. 



§ Von Meyer, Palaeontographica, 1860, p. 123. 



11 Cope, American Naturalist, 1880, p. 141. 



