SliaUs of Domestic [[ir.-ies and Quaggas. 517 



doubtful value as a basis tor the formation of natural <^roups, 

 for funetionless vestiges have seldom much importaiiee in 

 taxonomy/' This was written on the assumption of the 

 correetuess of the claim that the depression is the remains 

 or vestige of the much larger pit which, in more archaic 

 forms, e g. Hipparion, lodged, it is held, a facial gland com- 

 parable to that of Cervida?. My conclusion as to the 

 systematic value of the cliaracter in question was, and still 

 remains, I lelieve, quite sonnd, althongh I do not think the 

 hypothesis that lias been ()ut forward as to its signiticance 

 can be accepted as substantiated by the facts ; and, until we 

 get further evidence on the point, I incline to the view that 

 Sir William Flower was probably right in saying that no 

 trace of the preorbital depression seen in the skull of 

 Hipparion is to be found [in the adults] of any of the existing 

 species of Equidie. 



For the purpose of testing the frequency of the presence 

 of this depression in horses and of ascertaining, if possible, 

 by rough dissection, if any gland be discoverable over the 

 spot, I examined this area of the skull in several horses 

 slaughtered in the Zoological Society's Gardens for food. 



My methods of investigation were not precise enongh to 

 justify a denial of the existence of a vestige of a gland ; but 

 1 failed to detect any difference between the subcutaneous 

 tissue overlying the depression when it was present and that 

 overlying the corresponding area of the skull when it was 

 absent. As for the depression itself, it is sometimes present, 

 but more often absent : it exhibits, indeed, every gradation 

 between a hollow perceptible to the eye and touch and a 

 perfectly flat bony surface. From this hollow or from the 

 corresponding area of the skull arises a long muscle which 

 passes forwards to supply the upper lip and nose; and I 

 believe that its sole significance is to give au increase of 

 surface for the attachment of muscular fibres. If this be so, 

 variation in the extent to which the depression may be 

 developed is exactly what would be expected. 



It is possible, but hardly, I think, probable, that the very 

 large preorbital pit in Hipparion was also an area for muscular 

 attachment, lis appearance and structure suggest no such 

 function; and there is practically nothing in the formation 

 of the naso-premaxillary region of the skull pointing to the 

 possession by this extinct equine of a larger or more flexible 

 upper lip, requiring an increased muscular sup^ily, than is 

 found in recent members of the family. 



On the other hand, a comparison between casts of the 

 skulls o^ Hipparion and Onohippidimn forcibly suggests that 



