0» LECTURE V. 



to tlieir neural arches, in which the typical characters of the vertebra 

 are least departed from. 



The vertebrjB of the head are usually enumerated in a direction 

 contrary to those of the trunk, because, like the vertebra3 of the 

 tail, they lose their typical character as they recede from the com- 

 mon centre.* The names of the cranial vertebrte are taken from 

 those applied in Authropotomy to the bones composing their neural 

 spines, and the names of the neural arches from the significant terms 

 lately given (xxii. t. i. p. 145.), to the primary segments of the 

 brain, which they respectively protect. 



Each cranial vertebra, or natural segment of the skull, is divided 

 into a neural arch, with which the centrum and parapophyses are 

 always more immediately connected, and a hcemal arch with its 

 appendages. 



The neui'al arches are : — 



Nos. of component bones in the Cuts, 



I. Epencephalic arch (1, 2, 3, 4); 



II. Mesencephalic arch (5 to 8) ; 



III. Prosencephalic arch (9 — 12) ; 



IV. Rhinencephalic arch (13 — 15). 



The hfemal arches are : — 



i. Scapular, or scapulo-coracoid (50 to 52) ; 



ii. Hyoid, or stylo-hyoid (25, 38 to 43); 



iii. Mandibular, or tympano-mandibular (25 — 32) ; 



iv. Maxillary, or palato-maxiUary (20 — 22). 



The appendages of the hjemal arches are : — 



1. The Pectoral (54 to 57) 



2. The Branchiostegal (44) 



3. The Opercular (34—37) 



4. The Pterygoid (23, 24), 



B. The bones of the splanchno-skeleton constitute : — 



The ear-capsule or petrosal, and otolite (16, 16''); 

 The eye-capsule or sclerotic, and pedicle (17) ; 

 The nose-capsule or ajthmoid, and turbinal (18, 19) ; 

 The branchial arches (45 — 49). 



* We find the leading condition of these terminal modifications of the vertebral 

 column in the fact, that the contained nervous axis shrinks and recedes centripetally 

 at both ends. 



