294 , DR. E. HAT LANKESTER ON OKAPIA. 



of the nasals in Okapia) ; (5) median frontal growth (in Giraffa) ; and (G) median 

 parietal growth (in Uelladotherium, text-fig. 4, p. 285, m.f.l.). It is not in every case 

 that these " bosses " or " tumescences " of the skull-wall have gone on to form well- 

 marked " ossicusps," still less have they always given rise to an ossicusp of such size 

 anil importance that it lias acquired an independently ossifying cap or epiphysis. The 

 occipital exostoses of the five-horned Giraffe are well-marked knobs, but do not appear 

 to have independent ossification. On the other hand, the paired parietal and median 

 frontal horns of the Giraffe are prominent conical elevations of the outer plates of the 

 parietal and frontal bones respectively, separated by large air-sinuses from the deeper 

 plate and " capped " (but not by any means solely constituted) by superficial cones of 

 bony matter, which ossify independently of the tumescence or boss of the cranial bone 

 on which they rest (see text-fig. 12, p. 29.3). 



An interpretation of the separate ossification of these pieces and of the early 

 independence or separation of the ossicusps in the Bovidee appears to find flavour Avitli 

 many zoologists, which I regard as erroneous. It is supposed that these bony pieces 

 have not originated from the skull, but are ancestrally independent dermal bony plates 

 which become fused to the skull. I think that this is an erroneous interpretation of 

 the facts. On the contrary, I think that just as the marked and outstanding processes 

 of other bones in the mammalian body (such as trochanters, vertebral apophyses, &c.) 

 acquire independent ossification, and appearing as " epiphyses " ultimately fuse with 

 the bone of which they are in reality and origin only outgroioths (apophyses), so do 

 the ossicusps of the Pecorine horns acquire in many cases an independent formation, 

 which is related to their great size and importance, and is not a retention or exhibition 

 of ancestral independence. It is obvious that our whole view of the relations of the 

 " horns" of the Pecora to one another depends on the answer to this question — " Can 

 a cusp-like outgrowth of a cranial bone, developed in continuity with that bone, be 

 the genetic equivalent of a cusp-like structure which has in late embryological stages 

 a detached appearance and an independent ossification, and becomes only after such a 

 period of separateness united to the subjacent cranial bone 1" An investigation of the 

 embryological facts in the Bovidee at a stage earlier than that described by Brandt ', 



' See A. Brandt, " Ueber Horner und Geweihe," Festschrift Leuokarts, 1892. Eecentlj' Dr. J. Ulrich 

 Diirst has published a valuable essay, entitled, " Versuch einer Entwickelungsgeschichte der Horner der 

 Cavieornia," in the Festschrift zur Feier des 70. Geburtstages von Prof. Dr. Ad. Krsemar (Frauenfeld, 1902), 

 for the opportunity of seeing which I am indebted to Dr. Forsyth Major. Among the more important points 

 established by Diirst is the fact that the separated rudiment of the horn-core which appears in j'oung Bovidae 

 is not cartilage (as sometimes asserted), but, as one would have supposed, osteogenetic tissue. 



It seems that we still do not possess a really thorough histological and embryological study of the ossicusp 

 or bone of the horn and antler of Pecora. 



I venture (as modifying somewhat what I have said in the body of this memoir) to put forward the 

 hypothesis that whilst the primitive element of the ossicusp is an outgrowth of the outer table of a cranial 

 bone, a secondary accessory bony clement has been developed upon and in connection with this which has a 



