250 " REPORT—1846. 
The names printed in roman type signify those parts which, being usually 
developed from distinct and independent centres, I have termed ‘ autoge- 
nous’ elements. The italics denote the parts, more properly called pro- 
cesses, which shoot out as continuations from some of the preceding elements, 
and are termed ‘exogenous’: e.g. the diapophyses or upper ‘transverse 
processes,’ and the zygapophyses, or the ‘ oblique’ or ‘articular processes’ of 
human anatomy. 
The autogenous processes generally circumscribe holes about the centrum, 
which, in the chain of vertebrae, form canals. The most constant and exten- 
sive canal is that (fig. 14, 2) formed above the centrum, for the lodgment of 
the trunk of the nervous system (neural axis) by the parts thence termed 
‘neurapophyses. The second canal (fig. 14, 2), below the centrum, is in 
its entire extent more irregular and interrupted ; it lodges the central organ 
and large trunks of the vascular system (hemal axis), and is usually formed 
by the laminz, thence termed ‘hzmapophyses.’ At the sides of the cen- 
trum, most commonly in the cervical region, a canal is circumscribed by the 
pleurapophysis or costal process, by the parapophysis, or lower transverse 
process, and by the diapophysis, or upper transverse process, which canal 
includes a vessel, and often also a nerve. 
Thus a typical or perfect vertebra, with all its elements, presents four 
canals or perforations about a common centre; such a vertebra we find in 
the thorax of man and most of the higher classes of vertebrates, also in 
the neck of many birds. In the tails of most reptiles and mammals, the 
hemapophyses (as in fig. 14) are articulated or anchylosed to the under 
part of the centrum; space being needed there only for the caudal 
artery and vein. But where the central organ of circulation is to be 
lodged, an expansion of the hzmal arch takes place, analogous to that which 
the neural arches of the cranial verte- Fig. 15 
bre present for the lodgment of the 
brain. Accordingly in the thorax, the 
pleurapophyses (fig. 15, pl) are much 
elongated, and the heemapophyses (fig. 
15, h) are removed from the centrum, 
and are articulated to the distal ends 
of the pleurapophyses ; the bony hoop 
being completed by the intercalation 
of the hemal spine (fig. 15, As) be- 
tween the ends of the hemapophyses. 
And this spine is here sometimes as 
widely expanded (in the thorax of birds 
and chelonians, for example) as is the 
neural spine (parietal bone or bones) 
of the middle cranial vertebra in mam- 
mals. In both cases, also, it may be 
developed from two lateral halves, and 
a bony intermuscular crest may be ex- 
tended from the mid-line, as in the 
skull of the hyzna, and the breast-bone 
of the bird (fig. 15, hs). To facilitate 
the comparison of the merits of the 
preceding view and nomenclature of 
the typical vertebra with those of other 
comparative anatomists, I have thrown 
the results into the form given in 
Table II. 
Natural typical vertebra: thorax of a bird. 
