ANATOMY OP VERTEBKATES. 113 



palatomaxillary arch : they rest below upon the presphenoid and 

 vomer, support above the fore part of the frontal and the back 

 part of the nasal bones, and, by their outer or facial extension, 

 give attachment to the large antorbital or lacrymal bone. They 

 are ossified in and from pre-existing cranial cartilage. 



Such are the essential characters of the bones which Cuvier has 

 called ' frontaux anterieures ' * in Fishes, and to which I apply the 

 name of ' prefrontal ' in all classes of Vertebrate animals. In the 

 Cyprinoids, and most Halecoids, the prefrontals form part of an 

 interorbital septum. When anchylosis begins to prevail in the 

 cranial bones of Fishes, the prefrontals manifest their essential 

 relationship to the vomerine and nasal bones by becoming confluent 

 with them : thus we recognise the prefrontals in the confluent 

 parts of the nasal vertebra of the Conger, by the external groove 

 conducting the olfactory nerves to the nasal capsules, and by the 

 inferior process from which the palatine bone is suspended. 2 In 

 the Murcence, also, the prefrontals are plainly confluent with the 

 nasal, 15, bone, and form the well marked articular surfaces for the 

 palato-maxillary bone. In some fishes a process of the prefrontal 

 circumscribes- the foramen by which the olfactory ' crus ' finally 

 emerges from the anterior prolongation of the cranio-vertebral 

 canal. In the Carp this part of the brain traverses a deep notch 

 on the inner side of the prefrontal, fig. 83, 14. In the Cod the 

 palatine arch is chiefly but not wholly suspended to the prefron- 

 tals. The right prefrontal is the smallest in the unsymmetrical 

 skulls of the flat-fishes. 



The nasal bone is usually single, and terminates forward in a 

 thick obtuse extremity. The anterior end of the nasal is deepest 

 in those Fishes which have a small maxillary arch suspended from 

 the cranial axis by vertical palatines, and which have a large 



1 'Dews, frontaux anterieures, qui donnent passage aux nerfs olfactifs, ferment les 

 orbites en avant, s'appuyent sur le sphenoide et le vomer, et donnent attache par une 

 facette de Ieur borde inferieure aux palatins.' — Lecons d" Anat. Comp. ii. 1837, p. 606. 

 Compare this enunciation of the essential characters of the anterior frontals with 

 Cuvier's descriptions of the bones to which he applies that name in other classes, and 

 with the variable determinations of the same bones by other anatomists — le lacrymal, 

 Geoffroy and Spix ; lamina cribrosa ossis ethmoidei of Bojanus ; seitliche relchbeine, 

 Meckel, Wagner. Without at present entering into the respective merits or demerits 

 of these determinations, I shall only state that the prefrontals, under whatever names 

 they are described, are essentially the neurapophyses of the nasal vertebra, and that 

 the failure in the attempt to determine the special homologies of these bones may, in 

 every case, be traced to the non- appreciation of their true general homology. 



2 In the Conger, Cuvier ' recognises the prefrontals as persistent cartilages. 



l Op. cit. (Xlll.), ii. p. 235, 



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