132 ANATOMY OF VERTEBRATES. 



In this figure the several bones of the head of the European 

 Box-terrapene (Emys EuropcBa, Wgl.) are represented, disarti- 

 culated, in a side view of their vertebral relations. Beneath the 

 Roman figure, I, are the centrum, i. neurapophysis, 2, neural 

 spine, 3, and parapophysis 4, forming the neural (epencephalic) 

 arch ; with the pleurapophysis, 51, and haemapophysis, 52, forming 

 the haemal (scapular) arch, with its appendage, of the occipital 

 vertebra. Beneath n are the centrum, 5, the neurapophysis, 

 6, the neural spine, 7, the parapophysis, 8, forming the neural 

 (mesencephalic) arch : from 8 is suspended by an unossified 

 pleurapophysis the hremapophysis, 40, the haemal spine, 41, with 

 the appendage, 47, of the haemal (hyoidean) arch of the parietal 

 vertebra. Under in are the neurapophysis, 10, neural spine, n, 

 and parapophysis, 12, forming the neural (prosencephalic) arch ; 

 with the pleurapophysis, 28, and composite haemapophysis, 29 32, 

 forming the haemal (mandibular) arch of the frontal vertebra, of 

 which the centrum is not an independent ossification. Beneath 

 IV are, the centrum, 13, the connate neurapophyses and neural 

 spines, 14, forming the neural (rhinencephalic) arch ; with the 

 pleurapophysis, 20, haemapophysis, 21, and haemal spine, 22, 

 forming the haemal (maxillary) arch of the nasal vertebra. The 

 diverging appendages, for the fixation of this haemal arch are 

 more developed than in Fishes, where it retains more of its 

 typical mobility. Besides the appendage, 24, of the pleurapo- 

 physis, there is now another, extending in two successive 

 segments, 26 and 27, from the haemapophysis. The splanchnic 

 ossicle, 16', is part of the acoustic organ : the circle of bones, 17, 

 belong to the visual organ. Such are the ' general homologies ' 

 of the bones of the chelonian head, in reference to the vertebrate 

 archetype, fig. 21. Compared with bones of the piscine head, 

 fig. 81, previously named and characterised, those of fig. 92 are : 



1. Basioccipital. 



2. Exoccipital. 



3. Superoccipital. 



4. Paroccipital. 



5. Basisphenoid. 



6. Alisphenoid. 



7. Parietal. 



8. Mastoid. 



9. Presphenoid (unossified). 



10. Orbitosphenoid (in great part cartilaginous), 

 n. Frontal. 

 12. Postfrontal. 



