222 report— 1846. 



cavity in the fish beautifully and closely repeated : the prosencephala part 

 opens freely by the aperture bounded by the orbitosphenoids (fig. 9, 10) into 

 the common orbital cavity (or), and the rhinencephalic division of the cranium 

 is prolonged, as a groove upon the under surface of the coalesced frontals 

 (ib. n) above the orbits, expanding as it advances, until it is arrested by a 

 boundary formed by two bones (ib. 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 line; 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 appeal^ 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 



* " II suffit en effet de placer une tete de mammifere, de ruminant par example, a cote 

 d'ime tete de crocodile, pour s'assurer qu'il s'est fait ici (' du frontal anterieur') un demem- 

 bremeut du frontal. On pourroit, sans rien deranger, dessiuer sur le frontal du mammifere 

 la suture qui existe dans le crocodile, et on detacheroit ainsi dans le premier un frontal 

 anterieur qui auroit la nienie position, presque la meme figure, et absolument le meme emploi 

 que dans le crocodile." — Ossem. Fossiles, v. pt. ii. p. 73. 



