30 



ported the petrosals and alisphenoids : the prr*phenoidal prolongation (t) articulated with 

 the orbiUwpbenoidn, and it terminates forward* by a cavity which reorirrd the pointed mil 

 of the Tome r. 



The ali*pkrnoub (,) were firmly articulated by broad sutural surfaces to the expanded 

 sides of the basiaphrnoid ; above which their bases almost met and immediately (iipportrd 

 ill.- third ventricle or me*enccpha]on, leaving an intenpaoe for it* pituitary prolongation, 

 which retted in a cavity or ' fella' of the basisphenoid. In the Cod the chief part of the in 

 geminal nerve panes out of the cranium by the anterior notch of the aliiphenoid. A part of 

 the vestibule and the anterior lemicircular cmnal of the acoustic labyrinth usually encroach 

 upon its inner concavity, whence some have deemed it to be the petrous bone. 



Tlir parietal* (r, r) would complete above the osseous cincture of the most expanded wg- 

 ment of the brain, but are separated from one another by the anterior prolongation of thr 

 superoccipital : they are nearly flat, and present a much smaller proportional site than in tin- 

 higher classes of Vertebrata : they were articulated to the mastoids outwardly and below, 

 to the superoccipital above, to the frontal and po*t frontal before, and to the paroccipital 

 behind. 



The mattoiti* (, ) bear the same relation to the mesencephalic bony girdle, which the par- 

 occipital* do to the epencephalic one ; and they project outwards and backwards further 

 than the paroccipitals, forming the second strong transverse process at each side of the cra- 

 nium. This process is developed from the outer margin of the mastoid : the inner side 

 of the bone is expanded and enters (lightly into the formation of the walls of the cranial, or 

 rather the acoustic cavity ; its inner, usually cartilaginous surface lodging part of one of thr 

 semicircular canals. Each mastoid was wedged into the interspace surrounded by the ex- and 

 par -occipital*, the petrosal, the alisphenoid, the parietal, the frontal and post frontal bones. 

 The projecting process lodged, above, the chief mucous canal of the head, and below, afforded 

 attachment to the epitympanic or upper piece of the bony pedicle, from which the mandibu- 

 lar, hyoid, and opercular bones are suspended : its extremity gives attachment to the strong 

 tendon of the dono-lateral muscles of the trunk. 



The basal piece of the third cranial cincture, which defends the prosencephalon, or cere- 

 bral lobes, is formed by the pretpkenmd (t), already described as connate with or produced 

 from the basisphenoid. The sides of the prosencephalon are defended by the ordilotptir- 

 nmdt (i, it) : these are small scmielliptic plates, separated from the presphenoid by the ali- 

 sphenoid, to which they were articulated below and behind, whilst above they were joined to 

 the frontal and postfrontal, completing the anterior part of the lateral walls of the cranium. 

 The rhinencephalic crara arc continued forwards above the superior interspace of the orfaito- 

 sphenoids ; and the optic nerves escape by their inferior intenpaoe. 



The/ron/0/ bone (11) completes the prosencephalic arch above, and enters into the forma- 

 tion of the cranial cavity, though its major part forms the roof of the orbits, which accessory 

 function is the chief condition of the great expanse of this neural spine in Fishes. It is here 

 single and sends up a median crest, which is united with that of the superoccipital. The 

 frontal* rest in a small part of their extent upon the orbitospbenoids, but are more con- 

 stantly articulated, anteriorly, to the nasal and prefrontals, and posteriorly, with the post- 

 frontal*, the parietal*, the mastoids, and the superoccipital. 



