KINETOGENESIS. 315 



angles, horns are developed. In members of both 

 groups horns have been developed over the orbits also 

 (Fig. 87), and in the Dinocerata on the extremities of 

 the nasal bones as well. These growths are all on 

 parts which are subject to especial irritation by contact 

 with other bodies, animate and inanimate. 



Among Artiodactyla, the deer (Cervidae) are espe- 

 cially distinguished by the periodical shedding of all 

 but the bases of their horns. Extinct forms found in 

 the Upper Miocene of the United States and France 

 (the Loup Fork series) furnish the explanation of the 

 origin of this remarkable peculiarity. In the genus 

 Cosoryx we find that the horns may or may not pos- 

 sess a burr near the base of the beam, like that of the 

 deer ; the same species being indifferently with it or 

 without it. This observation has been made on three 

 species, the C. necatus, C. furcatus and C. ramosus. 

 The following explanation of these facts has been pro- 

 posed by myself. 1 "From the facts of the case the 

 following inference may be derived, premising that it 

 is very probable that a genus allied to the present one 

 has given origin to the family of the deer. It is ob- 

 vious that the horns of (Dicrocerus) Cosoryx did not 

 possess a horny sheath as in the Bovidae, from the fact 

 of their being branched. As the sheath grows by ad- 

 dition at the base, the presence of branches which 

 necessarily obstruct its forward movement, would be 

 fatal to the process. There is much to be said in favor 

 of the view that the horns were covered with an integu- 

 ment, probably furred, as in the giraffe and young 

 stage in the deer. Thus there are grooves in the sur- 

 face of the beam for superficial blood-vessels, which 



1 U. S. G. G. Survey West of the zooth Mer., G. M. Wheeler : IV., Paleon- 

 tology, 1877, p. 348. 



