INTRODUCTION. & 



(1858) and * Elements of Comparative Anatomy ' (1865) have been elaborated, extended 

 and corrected, furnish a convenient set of terms, which will be employed in the present 

 memoir. 1 



The following table may be found useful to those who have not been able to 

 methodise for themselves the results of recent inquiries in this field : 



I. The Occipital segment. (From cartilaginous occipital ring, derived from plates 



investing notochord, the parachordals. ,) 2 

 Basi-occipital (axial). 

 Ex-occipital. 

 Supra-occipital [Dermo-supra-occipital]. 



II. Otic Bones (ossifications of Otic capsule). 



Opisthotic (about, generally below, the arch of the posterior canal). 

 Epiotic (arch of posterior canal) . 

 Pro-otic (fore-edge of capsule). 

 Sphenotic (ampulla and arch of anterior canal). 



Pterotic (ampulla and arch of horizontal canal). [Dermal bones frequently 

 unite with one or other of the periotic bones.] 

 *** The pro-otics may appropriate part of the investing mass and meet along the 

 middle line (as in the Salmon), so as to simulate a cranial sclerotome. 



III. Ossifications of Trabeculae cranii and lateral cranial wall (trabecular crest). 



Basi-sphenoid {axial). 



[Parasphenoid] . 



Ali-sphenoid. 



Pre-sphenoid (axial, absent in Fishes and Amphibia). 



Orbito-sphenoid. 



Mesethmoid (axial). 



Ectethmoid (pre-frontal). 



IV. Ossifications of Palato-pterygoid arch. (Upper segment of mandibular arch.) 



Mesopterygoid. 



Pterygoid. 



Palatal. 



1 The original memoirs may be consulted in the 'Philosophical Transactions' (1869 — 1877) and 

 'Zoological Transactions' (1877). See also ' The Morphology of the Skull,' by Parker and Bettany (1877). 



2 The notochord is invested by the parachordals, but in certain types (Lamprey, Shark, Skate, 

 Sturgeon, Bombinator, Pseudis) has its own sheath of cartilage. 



B 



