18 



iindissected fish. The right frontal, like the left, is 

 bounded by the frontal of the other side, supraoccipital, 

 parietal, sphenotic, alisphenoid, the prefrontal of its side 

 and median ethmoid, except that the left frontal does not 

 reach the median ethmoid. 



Left Frontal {L.Fr., figs. 1, 2, 3). — Takes no part in 

 forming- the interorbital ridge. Compared with the right 

 frontal it is broad from side to side and shorter from 

 before backwards. As shown in figs. 1 and 2, it sends otit 

 on the right a strong transverse process which overlaps 

 the dorsal surface of the right frontal. The forward 

 process on the left of the left frontal lying over the left 

 prefrontal, together with the posterior portion of the latter 

 bone, are lying apparently in a very anomalous position, 

 i.e., they are situated under the left eye instead of over it. 

 This, however, has been produced by the frontal growing 

 forwards, and the prefrontal growing backwards, after the 

 torsion of the cranium was an accomplished fact. It is 

 thus a precisely analogous case to the anomalous position 

 of the anterior extremity of the dorsal fin. 



Prefrontal [R. and L. P.Fr., figs. 1, 2, 3).— The left 

 prefrontal is in every respect larger than the right — due 

 apparently to the circumstance just mentioned. Both 

 contain in front some cartilage which is continuous with 

 what we have termed the ethmoid cartilage. Both also 

 are perforated by a foramen transmitting the olfactory 

 nerve to the olfactory laminae of the nasal organ, the left 

 foramen being perceptibly smaller than the right — due 

 to the left olfactory nerve being so much smaller than the 

 right. The left prefrontal fits by means of a long narrow 

 backward process into a groove on the dorsal surface of the 

 front end of the parasphenoid — a process entirely absent 

 on the right side. The articular surface for the lachrymal 

 is smaller on the left side, and similarly the process 



