220 MR. H. O. FORBES ON THE [Feb. 28, 



is quite possible that further information and more abundant 

 materials may cause a modification of this view " \ 



Sir William Turner, in his paper on Ziph'ms cavirostris and Meso- 

 plodon soiuerhyi, in the Trans. E. S. Edinburgh, vol. xxvi. p. 768, 

 says: — "In my description I have named the dense solid bar in 

 the middle of the beak the mesorostral bone. This bar corresponds 

 with the ' vomer ' of Cuvier, Gervais, and Gray, with the ' anterior 

 tuberosity of the vomer' of Fischer, with the ' continuation of the 

 pre-frontals forward to near the end of the premaxillaries ' of 

 Owen, and with the 'anterior prolongation of the ethmoid' of 

 Flower. "Whatever name be applied to it, there can be no doubt 

 that it is an ossification of the anterior end of the long cartila- 

 ginous bar, which in the Cetacea is prolonged forwards to the 

 end of the beak, and in relation to the sides and lower surface 

 of which the spout-like vomer is formed." And Sir William Flower, 

 in the paper I have already quoted from, continues: — "But 

 it must be observed that, although the cartilage appears to be 

 nothing more than a continuation forwards of the ordinary 

 mesethmoid lamina or septum of the nose, the ossification is 

 not a simple extension forwards of that which occurs in all 

 Cetacea (in all Mammalia, in fact) in the hinder or internarial portion 

 of the septum, but appears to be an independent production, 

 peculiar to the genera ^Jesojdodon, Ziphiits, and certain allied extinct 

 forms. It is separated by an interval (which appears to diminish 

 with age, but of which traces can be seen on the upper surface of 

 the rostrum near its base) from the true mesethmoid ossification. 

 It differs from the latter in being intensely hard and compact, 

 whereas the mesethmoid is, especially at its anterior part, some- 

 what spongy in texture. It differs also in showing strong 

 indications of being formed by a pair of lateral ossifications, united 

 in the middle line, as the upper surface in many parts and the 

 anterior apex show a marked median groove. I think it mil be 

 well therefore to adopt Prof. Turner's name of ' mesorostral ' 

 bone for this solid bar forming the centre of the rostrum, restrict- 

 ing mesethmoid to the part lying between the nares and a short 

 distance in front of them, which is ossified in the young animal 

 and in all other species of Cetacea " ^. 



An examination of the sections of young specimens of Meso- 

 plodon grayi and M. layardi in the light of what takes place 

 in Ziphius aivirostris, Berard'ms arnuxii, and OJymenia, and per- 

 haps in the fossil genus Choneziphius, will, I think, show satis- 

 factorily that the mesorostral consolidfition is not an ossification 

 of the mesorhiual or mesorostral cartilage, but is an upgrowth 

 in the rostral trough, formed by a proliferation of the osseous 

 tissue of that part of the vomer itself, and perhaps partly of the 

 premaxillaries, at all events not an ossification of the mesorostral 

 cartilage pure and simple, as occurs in Clymenia and Berardius. 



Before discussing the question of species, 1 shall trace from 



1 Tr. Z. S. vol. X. p. 419. = Tr. Z. S. vol. x. p. 420. 



