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PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 57. 



cation (fig. 6). In the adult or even the half -grown skull all traces 

 of this division are obliterated, and the processus gracilis itseK later 

 becomes firmly attached to the tympanic ring by bony union. 



In Solenodon this bone is represented apparently by a long, thin 

 spicule which protrudes forwards from the processus gracilis, to which 

 it becomes united in the adult. The processus gracilis likewise is 



firmly united to the tym- 



AidZl 



^ 



Fig. 6.— Erinaceus eueopaeus. After Parker. Mall., mal- 

 leus; Man. M., manuisrium of malleus; Pt. gr., processus 

 QRACLLis; Quad., quadrate; Sta., stapes; Ty., tympanic ring. 



panic rmg. 



In Centetcs ecaudatus 

 a considerable trace of 

 this bone is left, much as 

 in Gymnura, except that 

 it is more reduced in 

 size. It is very distinct 

 from the malleus, but in 

 the adult is coossified 

 with the tympanic. In 

 the embryo Parker rep- 

 resents a large element 

 in this situation ^ which 

 is developed independ- 

 ently in Meckel's cartilage in advance of the processus gracilis, and 

 which is separated from the tympanic and the malleus (fig. 7). From 

 the similarity of the appearances of these two elements in Gymnura 

 and Centetes, coupled with the embryological evidence from Parker 

 just cited, there seems to be no doubt that a separate and distinct 

 element exists. In 



other members of the ^ufa( Fr.^' 



Centetidae I have been 

 unable to discover any 

 traces of this element 

 in the adult at least. 

 These include Hemicen- 

 tetes, Ericulus, Micro- 

 gale. In a like manner 

 I have found no satis- 

 factory evidence of its 

 existence in any mem- 

 ber of the Chiysochloridae, although it may be said that there are 

 no young specimens upon which these observations were made. 



It is rather surprising that Galeopterus should retain so few traces 

 of these features in the adult skull, in view of the many marked 

 resemblances of its skull to that of Rhynclwcyon. For some unknown 

 reason the skull bones of Galeopterus coossify very early, so as to 



yi/a// 



Fig. 7.— Centetes ecaudatus. After Parker, hu, lncus; 

 Mall, malleus; Man. M., manubrium of malleus; Pr. gr., 

 processus GRAcais; Quad., quadrate; Sta., stapes; Ty., tym- 

 panic RING. 



> Philos. Trans. Royal Soc London, 1886, vol. 176, pi. 33, fig. 6. 



