446 ANATOjMY of VERTEBRATES. 



groove on the posterior margin. The tAvelfth rib is the longest, 

 measurino: three feet. In the nineteenth rib the articular surfaces 

 of the head and tubercle are almost confluent, and the shaft de- 

 creases in thickness distally : its length is one foot four inches. 



In the sacrum the articular surface for the ilium is formed by 

 the first three of the four coalesced vertebrae. The metapophyses 

 are distinct in the first two. The neural spines are long, strong, 

 and tubercular at the end ; the last curves very much backward. 

 The three interarticular cartilages between these four vertebras 

 lonof remain unossified. In the caudal series the neural canal 

 does not extend beyond the seventh vertebra. 



The little Hyrax has not fewer than twenty-nine, or even 

 thirty, dorso-lumbar vertebrae. In the twenty-two dorsal ver- 

 tebrae of the skeleton of H, capensis,^ the spines incline toward 

 the thirteenth, which is vertical, and indicates the centre of motion 

 of that part of the trunk. In their forms and proportions they 

 resemble those of the Rhinoceros. Seven or eight pairs of ribs 

 directly join the sternum, which consists of six bones. The meta- 

 pophysis commences on the third dorsal, and attains the outside of 

 the zygapophysis on the fifteenth : it exceeds the diapophysis in 

 length in all the posterior dorsals. In the eighth lumbar verte- 

 brae the diapophyses suddenly acquire great breadth, and gradually 

 increase in length to the last lumbar ; the metapophyses are con- 

 tinued throughout the series. No anapophyses are developed. 



The transverse process of the atlas is perforated vertically at 

 its fore part by the vertebral artery, which afterwards perforates 

 the neural arch. The hypapophysis developes a short process. 

 The simple transverse process of the dentata is perforated at its 

 base for the vertebral artery, and the neural arch is perforated on 

 each side by the second cervical nerve. The pleurapophysial 

 part of the transverse process is much expanded in the third to 

 the sixth cervical vertebrae inclusive : I have found it wanting on 

 the left side of the seventh vertebrjB, but present as a distinct 

 element, or rudimental cervical rib, on the right side, where it 

 completes the foramen for the vertebral artery. The sacro-caudal 

 vertebrae are fourteen in number, of which the first three articulate 

 with the ilia, and the four succeeding have transverse processes. 



In an extinct S. American Perissodactyle ( Macrauchenia),^ 

 the cervical vertebrae are remarkable for their length, as the 

 name implies ; also for the flattening of the terminal articular 

 surfaces, and the imperforate character of the transverse processes, 



' XLiv. p. 524, no. 3097. * xcv. p. 35, pis. v. vi. vii. 



