AXIS 



23 



vertebrae are occasionally wholly (Eight Whales) or partially 

 (many Whales, Jerboa, certain Edentates) welded into a com- 



FiG. 10.— Side view of axis of Dog. 

 X |. 0, OiloiitoicI process ; ^s, 

 posterior zygapopliysis ; s, spin- 

 ous process ; f, transverse pro- 

 cess ; V, vertebrarterial canal. 

 (From Flower's Osteolor/i/.} 



Fig. 11. — Anterior surface of axis 

 of Eed Deer, .x f . 0, Odon- 

 toid process ; jjrs, posterior 

 zygapopliysis ; sn, foramen for 

 second spinal nerve. (From 

 Flower's Osteolocjy. ) 



bined mass. Indications of this have even been recorded in the 

 human subject. 



The dorsal vertebrae vary greatly in number • nine {Hyper- 

 ooclon) seems to be the lowest number existing normally ; while 

 there may be as many as nineteen, as in Ceidetrs, or twenty-two, 

 as in HijTdj:. 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 Neolalaena, 

 as many as seventeen in Tursiops ; this group, the Cetacea, 

 contains the extremes. Nine lumbars are found in the Lemurs 

 Inclris 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 



