Vertebroid Homologies of the Cranium in Vertebralia. 51 



and flat portion extending downwards and backwards in 

 man, and, at the junction with its fellow of the other side, 

 gives support to the neural spine. On the edges of the 

 lamella the articulating surfaces, allowing a slight motion, 

 are met with. The extension of the epiphysis of the tubercle 

 has been described incorrectly as the transverse process, as 

 it is only connected with the centrum or vertebra by means 

 of the pedicle. 



3. The Neural Spine is formed by the extension of the 

 lamella meeting in a spine. Kestricting the term Vertebra 

 to the centrum, the neur-arcs form the metavertehw, while 

 the laminae developed on the ventral aspect converging to 

 the sternum form the prove rtebne. These are constructed 

 on the same plan as the neur-arcs, and may be called Hcem- 

 arcs, as enclosing the trunk and main branches of the vas- 

 cular system. 



The Hsera-arcs also consist of three parts — 



(I.) Pedicle, or head and neck of the rib, normally articu- 

 lated opposite the intervertebral space, partly on each of 

 the adjoining vertebra?, and protecting the trunk of the 

 spinal nerve issuing from the neural tunnel beneath it. 



(2.) The lamella or body of the rib ; its tubercle rests on 

 that of the neur-arc of the next lower vertebra. 



(3.) The spine or cartilage of the true ribs is attached to 

 the sternum, where it exists, or coalesces in the median line. 



It may also be assumed that there exists a provertebral 

 stem or prokaulon as exhibited in the sternum of mammals, 

 birds, and reptiles, which Geoffroy St Hilaire termed Sterne- 

 brce, as well as metahaulon, or dorsibrw, represented in the 

 interspinous bones of ichthyia or osseous fishes. 



The splanchno-skelon, represented by the hyo-branchio- 

 stegal and branchial system, belongs to the prokaulon or 

 provertebral system, which includes the prothoracic, rneso- 

 thoracic, and metathoracic wings of the insect and the ven- 

 tral fins of fishes. 



The provertebral trunk of mammals consists of there kistse 

 or thoraces. 



I. Prothorax or prosopo-kista includes the bones of the 

 face or mandible. 



