PLATE XLV 



Ontogenesis of the Horns of Domestic Cattle 



Development of the horny sheath and the osseous horn in seven stages. Drawn from preparations made by S. H. Chubb, in the 

 collections of the American Museum of Natural History. 



A, Foetal skull, approximatelj- in the fifth month of the intrauterine growth. The future horn area is indicated by a thickening of 



the epidermal cells, from which arise 40 scattered hairs (first stage of the hair tuft) . 



B, Foetal skuU approximateh' of the sixth or seventh month. Epidermal thickening enlarged, covered with the pointed and partly 



agglutinated hair tuft (beginning of the horn sheath). 



C, Foetal skull of the ninth month, in which first appears the osseous horn rudiment covered with a cap of thickened epidermis 



and a rudiment of the horn sheath of the agglutinated hairs. 



D, Skull of calf two weeks after birth, in which the osseous horn and the horn sheath are shifting back toward the occiput, through 



the ontogenetic allometric development of the frontals and recession of the parietals. 



E, Skull of calf two months after birth, showing the allometric shifting of the small osseous horn and the horn sheath toward the 



occiput. 



F, Yearling skull of 18 months, in which the osseous horn and the sheath are fuUy shifted back upon the occiput. 



G, Adult skull of the ninth year, showing the completed osseous. 



