FOSSIL MAMMALIA. 



37 



Giraffe, the inferior transverse processes are represented by relatively smaller 

 compressed lamina?, projecting obliquely downwards and outwards from the an- 

 terior and inferior extremity of the body of the vertebra. The superior trans- 

 verse processes in this animal are very slightly developed in any of the cervical 

 vertebra;, and the perforation for the vertebral artery is above and generally in 

 front of the rudiment of this process, being continued as it were through the side 

 of the substance of the body of the vertebrae. 



In the long cervical vertebrae of the Camel and Llama, the upper and lower 

 transverse processes are not developed in the same perpendicular plane on the 

 sides of the vertebra?, but at some distance from each other ; the lower transverse 

 processes (a, fig. 1, PL VI.; a, fig. 1, 3, 4, PI. VII.) being given off from the lower 

 part of the anterior extremity of the body of the vertebra; the upper ones (b, fig. 1, 

 PI. VI. ; a, fig. I, 3, 4, PI. VII.) from the base of the superior arch near the pos- 

 terior part of the vertebra, or from the sides of the posterior part of the body of 

 the vertebras. The extremities of these transverse processes do not become united 

 together, but they either pass into each other at their base, or continue throughout 

 life separated by an oblique groove (as in fig. 1, PI. VI.) This groove would not, 

 however, afford sufficient defence for the important arteries supplying those parts 

 of the brain which are most essential to life ; and, accordingly the vertebral 

 arteries here deviate from their usual course, in order that adequate protection 

 may be afforded to them in their course along the neck. From the sixth to the 

 second cervical vertebras inclusive in the Auchenice, and from the fifth to the second 

 inclusive in the Cameli* the vertebral arteries enter the vertebral canal itself, along 

 with the spinal chord, at the posterior aperture in each vertebra, run forwards 

 on the outside of the dura mater of the chord between it and the vertebral arch, 

 and when they have thus traversed about two-thirds of the spinal canal, they 

 perforate respectively the superior vertebral laminae, and emerge directly beneath 

 the anterior oblique or articulating processes, whence they are continued along 

 with the spinal chord into the vertebral canal of the succeeding vertebra, and 

 perforate the sides of the anterior part of the superior arch in like manner ; and 

 so on through all the cervical vertebras until they reach the atlas, in which their 

 disposition, and consequently the structure of the arterial canals, resemble those 

 in other Ruminants. 



The two cervical vertebras of the Macrauchenia present precisely the struc- 



* In the seventh cervical vertebra of the Camel, as in many other Mammalia, there is no perforation in 

 any part for the vertebral arteries. In a Vicugna, I find the same structure ; but in a Llama, the side of the 

 body of the seventh cervical vertebra is perforated longitudinally on the right side. In the Camel, the verte- 

 bral arteries pierce the sixth cervical vertebra, immediately below the superior transverse processes, and pass 

 obliquely to the anterior aperture of the cervical canal, where they emerge beneath the anterior oblique processes, 

 and then enter the spinal canal of the fifth cervical vertebra, as described in the text. 



