299 REPORT—1846. 
cavity in the fish beautifully and closely repeated: the prosencephalice part 
opens freely by the aperture bounded by the orbitosphenoids (fig. 9, 10) into 
the common orbital cavity (07), and the rhinencephalic division of the cranium 
is prolonged, as a groove upon the under surface of the coalesced frontals 
(ib. 11) above the orbits, expanding as it advances, until it is arrested by a 
boundary formed by two bones (7d. 14), which rest below upon the vomer 
and give attachment there to an ascending process of the palatines (20), which 
sustain by their mesial and upper expanded surfaces the nasal (15) and fore- 
part of the frontal (11); and articulate exteriorly with the large lacrymal 
bone (fig. 22,73) perforated as in the fish and serpent by a mucous duct from 
the orbit. They are each grooved on their inner or mesial surface (indicated 
by the numerals 14, in fig. 9) by the olfactory nerve, where it escapes from 
the cranium to spread upon the membranes sustained by the cartilaginous 
capsules anterior to the bones in question; below these grooves the bones 
(14) extend inwards and meet at the mesial linc; but do not coalesce there 
as in the frog, nor extend their mesial union upwards, so as to convert the 
olfactory grooves into two complete canals. They, therefore, retain or resume 
much more of their primitive piscine character than do their homologues in 
the frog or serpent, and manifest it conspicuously by developing a subtrian- 
gular external plate which appears on the upper surface of the cranium at 
the anterior angle of the orbit between the frontal, the lacrymal and the 
nasal bones. In short, the homology of the bones 14 in the crocodile (figs. 9, 
21, 22) with those so numbered in the fish (figs. 4 and 5), was quite unmis- 
takeable ; and, with the exception of Spix, all anatomists have concurred in 
this respect with Cuvier: only some of them have extended further and 
expressed differently the homologies of the bones in question. 
Now, bearing in mind the small brain of the cold-blooded crocodile, and 
the concomitantly restricted development of the spine or roof-bone in special 
relation with the cerebrum, viz. the frontal (11), which is aided in its se- 
condary function in relation to the orbit by distinct supraorbital bones in all 
crocodiles, and contrasting the condition of the part of the brain which, 
chiefly governs the development of the frontal bone with that of the same 
division of the brain of mammalia,—-let us proceed to make the comparison 
which Cuvier recommends*, in order to trace the homologues of the croco- 
dile’s prefrontals in the mammalian class. 
We place the skull of a ruminant (the red deer, e. g.) by the side of that 
of a crocodile, and delineate a suture which would detach a portion from the 
frontal, having the same superficial connections as the upper peripheral plate 
of the prefrontal has in the crocodile. It appears to be far from presenting 
the same figure; but most assuredly such artificially detached portion of 
the ruminant’s frontal has not the same functions (‘emploi’) as the pre- 
frontal has in the crocodile. For if we even include with the part so 
detached the anterior portion of the descending orbital plate of the frontal, 
we find it joining below the orbitosphenoid without any connection with the 
vomer, or any attachment to the palatine: it forms no immediate part of the 
supporting plate of the rhinencephalon, nor of the foramina for the exit of 
the olfactory nerves. Such artificially detached portions of the mammalian 
frontal are entirely separated from each other; whilst one of the important 
* “T] suffit en effet de placer une téte de mammifére, de ruminant par example, a cdté 
d’une téte de crocodile, pour s’assurer qu’il s’est fait ici (‘ du frontal antérieur’) un démem- 
brement du frontal. On pourroit, sans rien déranger, dessiner sur le frontal du mammifére 
la suture qui existe dans le crocodile, et on détacheroit ainsi dans le premier un frontal 
antérieur qui auroit la méme position, presque la méme figure, et absolument le méme emploi 
que dans le crocodile.”—Ossem. Fossiles, y. pt. ii. p. 73. 
