98 LECTURE V. 



has undergone more modification than any of the preceding bones in 

 connection with the general distortion and loss of symmetry of the 

 head : in the Holibut the right posterior angle is truncated, and the 

 rest of that side scooped out, as it were, to form the large orbit of 

 the right side : the left side of the bone retains its normal form : a 

 median crest, a continuation of that upon the supra-occipital, divides 

 the two sides. The frontal is developed in and from the perichon- 

 drium and the membrane closing the upper fontanelle in the primitive 

 cartilaginous cranium. 



The post-frontah (parapophyses* of the frontal vertebra, figs. 

 30. 33. 12, 12) obviously belong to the same category of vertebral 

 pieces as the mastoids, whose prominent crest they partly underlie 

 and complete, lending their aid in the formation of the single (<?. g. 

 Cod, Salmon), or double {e. g. Pike) articular cavities for the tym- 

 panic pedicle : like the mastoids they are ossified in and from the 

 primitive cranial cartilage; and their inner surface is expanded, but 

 this less frequently enters into the formation of the cranial cavity : 

 they form the posterior boundary of the orbit ; are articulated below 

 to the orbito-sphenoid and ali-sphenoid, above to tlie frontal, and by 

 their posterior and upper surfaces to the mastoid. The ai'ea included 

 by the prosencephalic cincture is widely open anteriorly, correspond- 

 ing with the great anterior membranous fontanelle in the Sharks, but 

 this relates more essentially to the fact of the true cranial or neural 

 canal not being terminated by the frontal vertebra. 



The circle of bones f which completes the axis of the skull an- 

 teriorly, and protects the olfactory chords or ganglions, consists of 

 the ' vomer ' below, the ' pre-frontals ' laterally, and the ' nasal ' above 

 ifig.M.). 



The vomer (centrum of nasal vertebra, 

 figs. 30. and 34. 13) is thick and ex- 

 panded anteriorly, slender, and terminating 

 in a point posteriorly, wiiere it is wedged 

 into the under part of the pre-sphenoid ; its 

 antero-lateral angles are articulated to the 

 ,^ T pre-frontals ; its upper surface supports the 



Disarticulated neural arch of n'lsai ^asal bouc, somctimcs immediately, some- 



vortcbra: viewed trom behind. ' ./ ' ^ 



{Gadus Morrhua.) timcs by an intervening ethmoidal cartilage. 



* The position of the transverse processes fpar-occipitals, mastoids, and post- 

 frontals] of the foregoing cranial vertebra;, would seem to indicate them to be upper 

 ones (diapophyses) rather than lower ones (parapo])hyses) ; but I know not any 

 example of diapojihyses developed as independent, autogenous, vertebral elements ; 

 and we see the parapophyses of the trunk gradually ascending in position, as they 

 advance towards tlie head, in fishes. 



f The " vertebra olfactoria" of Bojanus, who, however, regards the spine as the 

 " liimina media rothmoidei." 



