ARCHETYPE OF THE SKELETON. 31 



proper centrum and neural arcb, as in Fig. 21, Nos. 51, 

 53, 57. 



The four anterior neurapopliyses, 14, 10, 0, 2, give issue 

 to the nerves, the terminal modifications of which consti- 

 tute the organs of special sense. 



The first or foremost of these is the organ of smell, 19, 

 always situated immediately in advance of its proper seg- 

 ment, which becomes variously and extensively modified 

 to inclose and protect it. 



The second is the organ of sight, 17, lodged in a cavity 

 or " orbit" between its own and the nasal segment, but 

 here indicated above that interspace. 



The third is the organ of taste, the nerve of which 

 perforates the neurapophysis, 6, of its'proper segment, 

 called " parietal vertebra," or passes by a notch between 

 this and the neurapophysis, 10, of the frontal vertebra, 

 to expand in the organ, which is always lodged below, 

 in the cavity called " mouth," and is supported by the 

 haemal spine, 41, hs, of its own vertebra. 



The fourth is the organ of hearing, 16, indicated above 

 the interspace between the neurapophysis of its own 

 (occipital) and that of the antecedent (parietal) vertebra, 

 in which it is always lodged; the surrounding vertebral 

 elements being modified to form the cavity for its recep- 

 tion, which is called " otocrane." The jaws are the modi- 

 fied hasmal arches of the first two segments. 



The mouth opens at the interspace between these h^mal 

 arches; the position of the vent varies (in fishes), but 

 always opens behind the pelvic arch, S, 62, 63, ^, when 

 this is ossified. 



Outlines of the chief developments of the dermoskeleton 

 in different vertebrates, which are usually more or less 

 ossified, are added to the neuroskeletal archetype; as, 



