266 report — 1846. 



The neural spine commonly retains in the trunk the form indicated by its 

 name ; but in the atlas of the crocodile, where it is distinct from the neur- 

 apophyses, it is a depressed plate. In the thorax and abdomen of chelonians 

 it becomes still more expanded and flattened, and its borders unite by dentated 

 suture to contiguous spines and to the similarly expanded pleurapophyses. 

 The neural spine is absent in the thin annular cervicals of the mole ; it is 

 unusually developed and forms a thick square columnar mass of bone in the 

 cervicals of the opossum. It is double in the anterior vertebrae of some 

 fishes : in the barbel one stands before the other ; in the tetrodon they 

 stand side by side : and various other minor modifications of this peripheral 

 element might be cited. 



The parapophyses of the trunk- vertebra? manifest their autogenous cha- 

 racter in fishes alone ; and in most species the character is soon lost, the par- 

 apophyses becoming confluent with the centrum ; and, in the tail, either with 

 the pleurapophyses also, or with each other and the haemal spine, thus comple- 

 ting the haemal canal (fig. 16). Amongst air-breathing vertebrates the par- 

 apophyses of the trunk-segments are present only in those species in which 

 the septum of the heart's ventricles is complete and imperforate, and here 

 they are exogenous and confined to the cervical and anterior thoracic vertebra?, 

 or to the sacrum (as in the ostrich, figs. 15 and 27, p). The parapophyses are 

 subject to a certain extent of variation as to form : they are either mere 

 tubercles; or simple, shorter or longer, transverse processes ; or they may take 

 the form of long plicated lamina? (in the tails of some pleuronectida?): they 

 are longer and broader than the pleurapophyses in the cod-tribe ; and are 

 sometimes much expanded in the anterior vertebra? of fishes, where they 

 ascend in position, and in the siluroid species above described, coalesce to 

 form a broad outstanding ridge, directed outwards and a little upwards, and 

 rising as they approach the cranium, where they are joined by close suture to 

 the paroccipitals. 



The normal function of the parapophyses is to give attachment to muscles 

 and articulation to ribs, and, occasionally, additional strength and fixation to 

 anchylosed portions of the vertebral column. As a rare and exceptional in- 

 stance, the expanded and excavated parapophyses of the second and third 

 vertebra? in the genus Cobitis perform an office closely analogous to one of 

 those of the mastoid in man, since they inclose air-cells brought into com- 

 munication with the acoustic labyrinth by a chain of small ossicles : and these 

 singularly modified rudiments of the swim-bladder seem to have no other func- 

 tion in the groveling loaches than that in connection with the sense of hearing. 



The pleurapophyses are less constant elements than the neurapophyses ; 

 they exist as free appendages or ' floating vertebral ribs ' in the trunk, and 

 sometimes at the fore-part of the tail, in fishes, serpents, and certain batra- 

 chians (fig. 28, pi). The atlas has its pleurapophyses in most fishes, but they 

 are often detached from their centrum, and sometimes joined to long bony 

 haemapophyses, as is well-seen in the Argyreiosus, and other deep-bodied 

 scomberoids. Ossified haemapophyses are not present in any other vertebra? 

 of the trunk in fishes. In batrachians the pleurapophyses of the single pelvic 

 vertebra are similarly connected with ha?mapophyses, and the costal arch is 

 there completed. In the nienoponie, the pleurapophysial element of the sacrum, 

 ib. pi', is ossified from two centres. Such typical vertebra? are more common 

 in the higher air-breathing classes. Here the pleurapophyses have generally 

 the long and slender form understood by the word ' rib ;' but they expand into 

 broad plates in the thorax of the apteryx, in the anterior thoracic vertebra of 

 whales, and more especially in the carapace of chelonians, where they are 

 joined to each other by suture, and also to the expanded neural spines. These 



