NECTURUS MACULATUS. 413 
deles the walls are formed by the cartilaginous trabeculae or in part by an 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 
posteriorly by a low ridge topographically continuous with them. The details of the 
separate bones are as follows : — 
1. rrontaL. 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 (ie fh Premaxiltary 
: R f rocess if Process 
form the longer and thinner parietal proc- “i \ p)'\ 
esses. A single frontal, isolated from its 
surroundings, resembles a flat and quite 
OLfactery 
Process. 
Fa 
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Fen, ih Unenate 
irregular splinter of bone from the under 
(ventral) side of which hangs a partially 
detached plate directed backwards, the 
processus uncinatus of Wiedersheim,’ which 
forms the anterior portion of the U-shaped 
ridge described above. The notch enclosed 
Margin im Contact with opposite Frontat, 
between this process and the main body of 
the bone transmits the olfactory nerve and 
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is converted into a foramen by the addition DORSAL 
of the antero-lateral process of the parietal 
tie tal—Protess, 
rela 
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Parietal process 
and the trabecula. A conspicuous proc- 
Rave 
ess upon the outer margin of the bone Gin ee ee ere 
in this region, directed backwards, and surfaces with other bones are designated by an x. 
seeming to belong to the uncinate process 
rather than to the main body of the frontal, assists also in the formation of the olfactory 
foramen and may be 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. 
