the central axis, the chain of little bones, the vertebrae, threaded
on the spinal cord (see Figure 1 and Section 1); the thorax, the box
enclosed by ribs and sternum; the fore-limb and bones connected
with it (pectoral girdle and limb), and the hind-limb and bones
connected with it (pelvic girdle). Finally there is the skull, but
following the London University syllabus, we shall substitute the
skull of the dog for of that of the rabbit, as more typically mammalian
(Section 4).
Section 77. In Section 3 (which the student should refer to) we have
a division of the vertebrae into four varieties. Of these most
representative is the thoracic. A thoracic vertebra (Figure 4, Sheet
5, T.V.) consists of a central bony mass, the body or centrum (b.),
from which there arises dorsally an arch, the neural arch (n.a.),
completed by a keystone, the neural spine (n.s.); and coming off
laterally from the arch is the transverse process (tr.p.). Looking at
the vertebra sideways, we see that the arch is notched, for the exit
of nerves. Jointed to the thoracic vertebrae on either side are the ribs
(r.). Each rib has a process, the tuberculum, going up to articulate
with the transverse process, and one, the capitulum articulating
between the bodies of two contiguous vertebrae. The facets for the
articulation of the capitulum are indicated in the side view by
shading. At either end of the body of a vertebra of a young rabbit are
bony caps, the epiphyses (ep.), separated from the body by a plane
of unossified cartilage (indicated, by the dots). These epiphyses to
the vertebral bodies occur only among mammals, and are even absent
in some cases within the class. In the adult rabbit they have ossified
continuously with the rest of the body.