NECTURUS MACULATUS. 



413 





deles the walls are formed by the cartilaginous trabeculae or in part by au ossification in 

 these elements, the orbito-sphenoid. A foramen for the olfactory nerve is formed at 

 the junction of the frontal and parietal contributions to this ridge; other nerves, as 

 the trigeminus and facialis, emerge from the cranial cavity just posterior to it, but the 

 nerves to the eye muscles and the opticus pass through tiny foramina, running very 

 obliquely through the process itself. 



The floor of the brain case is formed by the very extensive parabasal, which receives 

 upon its dorsal surface the lateral processes projecting from the roof, and reinforces them 

 postei'iorly by a low ridge topographically continuous with them. The details of the 

 separate bones are as follows : — 



1. FRONTAL. The frontals form a little more than a third of the dorsal surface of 

 the skull. They lie in contact with one another for about two thirds of their length, 

 diverging anteriorly to form a pair of short 

 premaxillary processes, and posteriorly to 

 form the longer and thinner parietal proc- 

 esses. A single frontal, isolated from its 

 surroundings, resembles a flat and quite 

 irregular splinter of bone from the iinder 

 (veiitral) side of "which hangs a partially 

 detached plate directed backwards, the 

 processus uncinatus of Wiedersheim,Vhich 

 forms the anterior portion of the U-shaped 

 ridge described above. The notch enclosed 

 between this process and the main body of 

 the Ijone transmits the olfactory nerve and 

 is converted into a foramen by the addition 

 of the antero-lateral process of the parietal 

 and the trabecula. A conspicuous proc- 

 ess upon the outer margm of the bone 

 in this region, directed backwards, and 

 seeming to belong to the uncinate process 



rather tlian to the main body of the frontal, assists also in the formation of the olfactory 

 foramen and may l)e termed the olfactory process. 



Upon the ventral side of the bone are seen two roughened ridges for the attachment 

 of other bones. Of these the more anterior is a curved ridge connecting the olfactory and 

 premaxillary processes and serving for the attachment of the vomer ; the other involves 

 the ventral surface of the uncinate process and comes in contact with the parabasal. 



1)0RSAL 



NTRAL 



Fig. l.S. Two view.s of riKht frontal. X 3. Contact 

 !-urfaces with other bones are designated by an x. 



