V ertebrotd 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. Eestricting the term Vertebra 
to the centrum, the neur-arcs form the metavertehrce, while 
the laminse developed on the ventral aspect converging to 
the sternum form the provertehrm. These are constructed 
on the same plan as the neur-arcs, and may be called Rcem- 
arcs, as enclosing the trunk and main branches of the vas- 
cular system. 
The Hsem-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 vertebrge, 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 provertehral 
stem or frolmulon as exhibited in the sternum of mammals, 
birds, and reptiles, which Geoffroy St Hilaire termed Sterne- 
hrce, as well as metakaulon, 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 
prevertebral system, which includes the prothoracic, meso- 
thoracic, and metathoracic wings of the insect and the ven- 
tral fins of fishes. 
The prevertebral trunk of mammals consists of there kistee 
or thoraces. 
I. Prothorax or prosopo-kista includes the bones of the 
face or mandible. 
