4.46 Zoological Society. 
Owen, and duly considered by him prior to. the publication of his 
work ‘On the Archetype and Homologies of the Vertebrate Ske- 
leton,’ 8vo, Van Voorst, 1848, from which he quoted the following 
passages regarding their true nature and homologies. Viewing them 
as processes from the cortical part of the centrum, Professor Owen 
states : ‘‘ The centrum may develope not only parapophyses, but in- 
ferior median exogenous processes, either single, like those of the 
cervical vertebre of saurians and ophidians (which in Deirodon scaber 
perforate the cesophagus, are capped by dentine, and serve as teeth*), 
or double (atlas of Sudis gigas} and the lower cervical vertebree of 
many birds); or the fibrous sheath of the notochord may develope 
a continuous plate of bone beneath two or more nuclei of centrums, 
formed by independent ossification in the body of the notochord, these 
nuclei being partially coherent to the peripheral or cortical plate.” 
(p. 96.) 
To this view Professor Owen had been led chiefly by the coexist- 
ence of these inferior exogenous processes in the anterior abdominal 
vertebre of certain fishes with the true hemal arches, the nature and 
modifications of which were so plainly demonstrated in the caudal 
region of fishes. Besides the species cited in which these ‘ proces- 
sus inferiores’ had been noticed by previous authors (Agassiz e. g. in 
the case of Sudis gigas), Professor Owen had discovered other modi- 
fications of the same nature, and referred to his description and figures 
of the confluent subvertebral processes in the anterior trunk-vertebre 
of the Bag ia tachypomus, a large siluroid fish (Vertebrate Archetype, 
p- 92, pl. 1. fig. 8; Annals of N Jatural History, vol. xx. 1847, p. 217, 
fig. 1): 
He had shown in his memoir on the so-called wedge-bones of the 
Enaliosauria, that the subvertebral processes in fishes were homolo- 
gous with those autogenous wedge-bones, with the exogenous infe- 
rior processes of the cervical and dorsal vertebre of ophidians and 
saurians, and with the body of the atlas in anthropotomy ; and in his 
work on the Archetype, Professor Owen had summed up his views 
of their nature in the following words: “The continuous bony plate 
supporting those centrums was perforated lengthwise by the aorta, 
offering another mode of formation of a heemal canal (c A), viz. by 
exogenous ossification in and from the lower part of the outer layer 
of the capsule of the notochord. The carotid hemal canal in the 
necks of birds seems to be similarly formed; and the neck of the 
ichthyosaurus derives additional strength and fixation from appa- 
rently detached developments of bone in the lower part of the cap- 
sule of the notochord, at the inferior interspace between the occiput | 
and atlas, and at those of two or three succeeding cervical verte- 
bree}. 
«The so-called ‘ body of the atlas’ in recent saurians, birds, mam- 
mals and man, is the homologue of the first of these subvertebral 
* Jourdan, cited in Cuvier’s Lecons d’Anat. Comparéé, ed. 1835, p. 340, and 
Odontography, p. 179. 
t Agassiz in Spix, Pisces Brasilienses, 4to, 1829, p. 6. tab. B. fig. 8 
t Sir Philip de M. Grey Egerton in Geol. Trans. Bad Ser. vol. v. p.” "187, pl. 14. 
