954 REPORT—1846, 
logues of the ‘ cdtes vertébrales’ of higher vertebrates, to which Geoffroy 
assigned the name ‘ paraaux,’ this appears to be another misapprehension of 
the relations in question. 
Development of vertebre.—Before applying the idea of the archetypal 
vertebra, or primary segment of the endo-skeleton, given in figs. 14 and 15, 
to the elucidation of the modifications of those segments in the different ver- 
tebrate classes, I shall premise a few observations on the mode of develop- 
ment of the vertebrze in those classes. 
The chief condition of the development of distinct vertebra in the trunk 
is the conjunction of nerves with, or their progress from the spinal chord : 
at least, this circumstance, with the concomitant exit of blood-vessels from 
the neural canal, seems to determine the development of the neurapophyses : 
and the vertebral bodies are not slow in coinciding in number with those im- 
portant arches; and in determining with the regular primary pairs of (inter- 
costal, lumbar, &c.) arteries, the inferior or hemal arches. We may learn how 
much the development of the neurapophyses and vertebral bodies depends, 
in the trunk, upon the conjunction of nerves with the spinal chord, by the 
fact that, in the regenerated tails of lizards, the vertebral axis remains con- 
tinuous and unjointed, because there is no co-extensive spinal chord giving 
off pairs of nerves. 
An extremely delicate fibrous band, with successively accumulated gelati- 
nous cells, compacted in the form of a cylindrical column, and inclosed by a 
membranous sheath, is the primitive basis, called ‘notochord’* (chorda dorsa- 
lis seu gelatinosa, Lat., gallertsdule und ruckensaite, Germ.), in and around 
which are developed the cartilaginous or osseous elements by which the 
vertebral column is established in every class of Myelencephala. 
The earlier stages of vertebral development are permanently represented, 
with individual peculiarities superinduced, in the lower forms of the class of 
fishest. In the Dermopteri or cyclostomous fishes, the neural and hemal 
canals are formed by a separation of the layers of the outer part of the apo- 
neurotic sheath of the gelatinous chorda: in the lancelet (Amphioxus) there 
is no distinction of structure in the cranial part supporting the anterior end 
of the neural axis, with which the trigeminal, optic and olfactory nerves com- 
municate, and the rest of the rudimental vertebral column: a labial carti- 
laginous arch supporting the tentacula is, at least, the only lineament of 
development which sketches out the skull. In the myxinoids the skull in- 
cludes a complex system of cartilages, but the vertebral column of the trunk 
has not advanced beyond the gelatino-aponeurotic stage. In the lamprey 
cartilaginous laminz are developed in the outer layer of the fibrous sheath, 
and give the first indication of neural arches{. In the sturgeons (Sturio, 
Polyodon) the inner layer of the fibrous capsule of the gelatinous notochord 
has increased in thickness, and assumed the texture of tough hyaline carti- 
lage. In the outer layer are developed distinct, firm, and opake carti- 
lages, the neurapophyses, which consist of two superimposed pieces on each 
side, the basal portion bounding the neural canal, the apical portion the 
parallel canal filled by fibrous elastic ligament and adipose tissue; above this 
is the single cartilaginous neural spine. The parapophyses are now di- 
stinetly developed, and joined tugether by a continuous expanded base, form- 
ing an inverted arch beneath the notochord for the vascular trunks, even in 
the abdomen. Pleurapophyses are articulated by ligament to the ends of the 
* Noros back, yopdn, string. We have hitherto had no English equivalent for this em- 
bryonic keel or basis of every vertebrate animal: ‘dorsal chord’ or ‘chorda’ is liable to 
be misunderstood for the ‘ spinal chord.’ 
+ Hunterian Lectures on Vertebrata, 1846, pp. 45, 46. 
t Cuvier, Mémoires du Muséum d’Histoire Naturelle, t. i. 1815, p. 130. 
