324 report— 1846. 



nections with the basioccipital (admitted by Agassiz to be a vertebral body) 

 behind, and with the alisphenoids above. 



In many fishes the basisphenoid unites with the basioccipital by a deeply 

 indented sutural surface, like that which unites together the elongated bodies 

 of the anterior trunk-vertebra? in the Fistularia. In mammals the basioc- 

 cipital and basisphenoid join each other by flat surfaces, also like the bodies 

 of the trunk-vertebrae, until the period when, in most of the class, the 

 joint is obliterated by anchylosis. These and similar repetitions of class- 

 characters of vertebral elements in the regions of the head and trunk are not 

 so wholly devoid of signification, as they must seem to be to the opponents 

 of the cranio-vertebral theory. 



In his new and elaborate classification of the bones of the skull of fishes, 

 M. Agassiz divides them primarily, like Cuvier, into bones of the cranium, 

 or ' box which envelopes the brain and the organs of sense ' : and into bones 

 of the face, 'which is composed of the moveable pieces subservient to nutrition 

 and respiration' (I. c. p. 110). 



This division is open to the objection that the bony or cartilaginous cap- 

 sules which immediately envelope the organs of sense are always originally, 

 and most of them permanently, separate from the box or capsule that enve- 

 lopes the brain. The independent character of the ear-capsules, for example, 

 is manifest on their first appearance in the ammocete ; and, although they 

 subsequently lose their distinctive features by the accumulation of cartilage- 

 cells around them in which the foundations of the neurapophyses and parapo- 

 physes, contributing to the otocrane, are laid, one centre of ossification is 

 commonly established, even in fishes, in special relation to the immediate 

 protection of the vascular and nervous parts of the labyrinth. 



As to the proper bony envelope of the eye, M. Agassiz does not enumerate 

 it amongst the cranial bones of fishes : but admits into that series only the 

 accessory protecting pieces which form the orbit ; or rather only those that 

 at the same time form the brain-case : for, the suborbitals, the entopterygoids 

 and palatines are placed amongst the 'facial' bones : whilst the supraorbi- 

 tals are transferred to another category of osseous pieces, the natural system 

 here prevailing over the artificial one. 



Subjoined* is an outline of the arrangement of the two primary classes of 

 ' cranial ' and ' facial ' bones, founded upon the embryological researches of 



* CRANIAL BONES. (OS CRANIENS.) 



A. EMBRYONIC BASIS (' BASE EMBRYONALE,' Vogt). 



a. Nuchal plate (' Plaque nuchale,' V.). Basioccipital, Exoccipitals, Paroccipitals, 



Supraoccipital, Petrosals. 



b. lateral loops (' Ames laterales,' V.). Alisphenoids, Orbitosphenoids. 



c. Facial plate (' Plaque faciale,' V.). Entosphenoid (l'ethmoide cranien, Ag.). 



B. PROTECTIVE PLATES {'PLAQUES PROTECTRICES,' V.). 



a. Superior plates. Parietals, Frontals, Nasals. 



b. Lateral plates. Prefrontals, Postfrontals, Mastoids (temporaux, Ag.). 



c. Inferior plates ('Plaque buccale,' V.). Basi- pre- sphenoid, Vomer. 



FACIAL BONES. (OS DE LA FACE.) 

 i. Maxillary arch. Suborbitals (jugaux, Ag.), Maxillary, Premaxillary. 

 ii. Palatine arch. Palatines, Entopterygoids, Pterygoids (transverses, Ag.). 

 in. Mandibular arch. Pretympanics (' caisses,' Ag.), Mesotympanics (' tynipano-mal- 



leaux,' Ag.), Hypotympanics (' os carres,' Ag.), Mandible. 

 iv. Hyoidean arch. Epitympanics (' masto'idiens,' Ag.), Preoperculars, Stylohyals, Epi- 



hyals, Ceratohyals, Basihyals (' l'os lingual,' Ag.). 

 v. vi. vn. viii. Branchial arches. ' Composes chacun de deux ou trois pieces et reunis 



sous le gorge par le corps de l'hyoide.' 

 ix. Pharyngeal arch. ' Compose d'une ou de plusieurs pieces,' &c. — Op. cit. t. i. 



pp. 124, 130. 



