II AXIS 
N 
Ow 
vertebrae are occasionally wholly (Right Whales) or partially 
(many Whales, Jerboa, certain Edentates) welded into a com- 
Fic. 10.—Side view of axis of Dog. Fre. 11.—Anterior surface of axis 
x §- 0, Odontoid process ; pz, of Red Deer. x#%. 0, Odon- 
posterior zygapophysis ; s, spin- toid process; pz, posterior 
ous process ; 7, transverse pro- zygapophysis ; sv, foramen for 
cess ; v, vertebrarterial canal. second spinal nerve. (From 
(From Flower’s Osteology.) Flower’s Osteology. ) 
bined mass. Indications of this have even been recorded in the 
human subject. 
The dorsal vertebrae vary greatly in number: nine (Hyper- 
oodon) seems to be the lowest number existing normally ; while 
there may be as many as nineteen, as in Centetes, or twenty-two, 
as in Hyrax. These vertebrae are to be defined by the fact that 
they carry ribs, and the first one or two lumbars are often 
“converted into” dorsals by the appearance of a small super- 
numerary rib. The spinous processes of these vertebrae are 
commonly long, and sometimes very long. It is only among the 
Glyptodons that any of these vertebrae are fused together into a 
mass. 
The lumbar vertebrae, which follow the dorsal, vary greatly 
in number. There are as few as two in the whale Neobalaena, 
as many as seventeen in Tursiops; this group, the Cetacea, 
contains the extremes. Nine lumbars are found in the Lemurs 
Indris and Loris. As a rule the number of lumbars is to some 
extent dependent upon that of the dorsals. It often happens that 
the number of thoraco-lumbar vertebrae is constant for a given 
group. Thus the Artiodactyles have nineteen of these vertebrae, 
and the Perissodactyles as a rule twenty-three. A greater 
number of dorsals implies a smaller number of lumbars, and of 
course vice versa. The existence of a sacral region formed of a 
