Botany and Zoology. 127 



transmitted to the four organs of special sense seated in the head- 

 Prof. Owen adopted the names which had been assigned to these ver- 

 tebrae from the bones constituting their neural spines, viz., occipital, 

 parietal, frontal, and nasal; and enumerated them from behind for- 

 wards, because, like the vertebrae of the tail, they lose their typical 

 character as they recede from the common centre or trunk. The gen- 

 eral results of the Professor's analysis may be thrown into the follow- 

 ing tabular form : — 



Primary Segments of the Skull-bones of the Endo-skeleton. 



VERTEBRJE. 



Centrums. 

 A>mt apophyses, 

 Neural Spines. 

 Par apophyses. 

 Pit ur apophyses. 



H&mapophyses. 

 Hesmul Spines. 



OCCIPITAL. 



Busioccipital. 

 Exoccipital. 



Su preoccipital. 



Paroccipital. 



Scapula 



Coracoid. 



Kpisternum. 



PARIETAL. I FRONTAL. 



Basisphenoid. Pre.cphenoid. 



Alisphenoid. 



Parietal. 



Mastoid. 



Slylohyal. 

 Ceratohyal. 



Orbitosphenoid. 

 Frontal. 

 Postfi octal. 

 Tympanic. 

 Articular. 



asihyal. Dentary. 



NASAL. 



Vomer. 

 Prefrontals. 

 Nasal. 

 None. 



Palatal. 



Maxillary. 



Premaxillary. 



diverging appendage.poxz-Mmb or fin. B/anchiosteijals. (Operculum. (Pterygoids cfeZygom.i. 



The upper or neural arch of the occipital vertebra protected the epen- 

 cephalon, or medulla oblongata and cerebellum ; that of the parietal 

 vertebra protected the mesencephalon , or third ventricle, optic lobes, 

 conarium and hypophysis ; that of the frontal vertebra the prosenceph- 

 alon, or cerebral hemispheres ; that of the nasal vertebra the rhinen* 

 cephalon, or olfactory crura and ganglions. 



I he superior development of the cerebral hemispheres in the warm- 

 blooded class, and their enormous expansion in them, occasions cor- 

 responding development of the neural spines, not only of their proper 

 vertebra, but, by their backward folding over the other primary seg- 

 ments, of those of all the other vertebra; whilst the more important 

 parts of the neural arch, as the neurapophyses, undergo comparatively 

 '"tie change. 



ihe acoustic nerve escapes between the occipital and parietal ver- 

 6 brae, but the organ itself is intercalated between the neural arches 

 °< these segments and its ossified capsule ; the petrosal projects into 

 the cranial cavity between the exoccipital and alisphenoid in the warm- 

 blooded vertebrata. The gustatory nerve (part of the third division of 

 the fif th pair) perforates or notches the alisphenoid, and in crocodiles and 

 "tony fishes passes through an intervertebral foramen between the ali- 

 sphenoid and orbitosphenoid ; but the gustatory organ is far removed 

 ,rom the neural arches or cranium proper, and is united with its fellow 

 t0 form the apparently single organ called the tongue. The optic 

 nerve perforates or Grooves the orbitosphenoid, and the eyeball in- 



tervenes between the frontal and nasal vertebra, as the earball 

 d °es between the occipital and parietal : the vertebral elements are 

 modified to form cavities for these organs of sense; that lodging the 

 eye being called the " orbit," that for the ear the " otocrane." 



The divergence of the olfactory crura, and the absence of any union 

 or commissure between the olfactory ganglia, leads to an extension of 

 J»fication from their neurapophyses, which are always perforated by 

 »« olfact OPy crura or nerves, to the median line between those parts; 

 ?!* the neurapophyses themselves coalesce together there in batrachia 

 blrd8 » and mammals. This extreme modification was to be expected 



