238 



PBOCEK DINGS OF THE 



[May, 1890. 



the Anatomy and Physiology of Vertebrates, although it is much greater than 

 in the Jerboa, a little rodent from Africa, which with the Chinchilla, is the 

 only other member of the family Jerloidce. This inclination forward is but 

 slight in the Jerboa, as compared with the Chinchilla, but Owen has mentioned 

 it only with reference to the first. It has been represented in the accompanying 

 woodcut. 



The second of these variations is the existence of 

 three sacral vertebrae instead of two as described by 

 Yarrell in the Proceedings of the Zoological Society 

 of London for 1830-31, This is believed to be the 

 first printed description of the animal, but I am 

 told by Prof. Oldfield Thomas, of the British Mu- 

 seum, (Nat. Hist.), that they have a skeleton of 

 Chinchilla in their collection which also shows three 

 sacral vertebrae. These can also be seen in the same 

 woodcut. 



The third and most striking variation is a cres- 

 cent shaped flat bone occupying the anterior half of 

 the outer edge of the external meatus of the ear. 



The skull of my specimen only shows this bone 

 on the side. This is due to the one on the right side 

 having heen cut away with the skin when this was 

 being rougly removed preparatory to the prepara- 

 tion of the skeleton, and the next day, when, on 

 further work upon the head, the existing bone was 

 observed, it was too late to recover the missing one. 

 It is a perfectly healthy ossification and is attach- 

 ed to the skull ligamentously. After a short soak- 

 ing in water it again becomes slightly movable on 

 the skull, as it was in Ufe. It is well shown in the 

 woodcut, and another drawing, twice the size, is added. It seems remarkable 

 that it never was noticed either by Yarrell or Owen, the latter of whom gives 

 two life-size woodcuts of the head in his work already mentioned. 



Before proceeding to give an opinion as to the purposes of this bone, I have 

 taken the precaution to write to several naturalists of known reputation, inclu- 

 ding Mr. J. A. Allen, of the American Museum, New York City, who kindly 

 examined the Zoological Record for twenty-five years in a vain search for a no- 

 tice of the bone, and Mr. G. B. Howes of London, England, who replies that 

 he is familiar with it " and with its like in other Hysiricomorpha. There are 

 two such in Cavia, and I believe them to be ossifications of the cartilaginous 

 meatus externus ". 



With regard to a description already in print, Mr. HoWes says that he is not 

 familiar with any such, and Prof. O. Thomas says: "Like him (Mr. Howes ) I 

 have seen the extra ear-bone myself, but cannot remember where there is a r'e- 

 scription of it. I have, however, a strong impression that I have seen it de- 



Slde view of Pelvis, 



witti Sacral and Lumlbar 



Vertebra. 



