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 vertebras, form canals. The most constant and exten- 

 sive canal is that (fig. 14, n) 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, /<), below the centrum, is in 

 its entire extent more irregular and interrupted ; it lodges the central organ 

 and large trunks of the vascular system (haemal axis), and is usually formed 

 by the laminae, thence termed ' haemapophyses.' 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 

 haemapophyses (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 haemal arch takes place, analogous to that which 



the neural arches of the cranial verte- 

 brae present for the lodgment of the 

 brain. Accordingly in the thorax, the 

 pleurapophyses (fig. 15, pi) are much 

 elongated, and the haemapophyses (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 haemal spine (fig. 15, hs) be- 

 tween the ends of the haemapophyses. 

 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 hyaena, 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. 



Fig. 15 



Natural typical vertebra : thorax of a bird. 



