1904.] Allen, External Ear Bone in Certain Rodents. 13? 



of it. He being unable to find any published account of such 

 a structure, either in the Chinchilla or other mammals, wrote 

 to various leading mammalogists and comparative anato- 

 mists on the subject but succeeded in obtaining no very defi- 

 nite information. Mr. G. B. Howes of London, in reply to 

 his inquiries, stated that he was familiar with it, and "with 

 its like in other Hystricomorpha. There are two such in 

 Cavia, and I believe them to be ossifications of the carti- 

 laginous meatus externus." Mr. Howes further stated that 

 he knew of no published description of this bone. Mr. Old- 

 field Thomas, in replying also to Dr. Manigault's inquiries, 

 said : ' ' Like him (Mr. Howes) I have seen the extra ear bone 

 myself, but cannot remember where there is a description of 

 it. I have, however, a strong impression that I have seen it 

 described somewhere, but by whom, and in what particular 

 animal I cannot recall." 



I had likewise searched carefully for some published ac- 

 count of this interesting feature, but had been able to find 

 only that given by Dr. Manigault, as cited above, until my 

 attention was called by Prof. W. B. Scott, the eminent 

 palaeontologist, to a paper by Dr. W. Peters on the genus 

 Pectinator, wherein it is mentioned. 



Dr. Peters, in describing the skull of Pectinator (Trans. 

 Zool. Soc. London, VII, Pt. V, 1871, p. 401) states: "The 

 tympanic bullae are also comparatively larger than in Cteno- 

 dactylus; but the meatus auditorius externus has the same 

 direction, and is in the same manner elongated by an in- 

 ferior semiannular osseus appendage, as in Ctenodactylus ." 

 Dr. Peters 's figure of this appendage (/. c., pi. 49, fig. 3) 

 shows that it closely resembles, in size and form, the same 

 structure in Heteromys. 



Mr. Wm. Yarrell, many years before, gave an account of 

 the anatomy of Ctenodactylus massonii Gray (P. Z. S., 1831, p. 

 44), in which he says: "The meatus auditorius is elongated, 

 forming a tube 2-ioths of an inch in length on the inferior sur- 

 face and lined with a dense pigment." But he says nothing 

 of this elongation being produced by the development of a 

 separate ossicle 



