38 



ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 





ture and disposition of the bony canals for the vertebral arteries which are pecu- 

 liarly characteristic of the Camelidae among existing Mammalia. In Plate VI. 

 fig. 2, the groove and orifices of the canal for the vertebral artery are shown in a 

 section exposing the spinal canal : in Plate VII. figures 1 and 3 exhibit the orifices 

 at the commencement of the arterial canals, as seen in a posterior view of the 

 vertebrae ; in figs. 2 and 4, the terminations of the same canals are shown, in the 

 anterior view of the same vertebrae ; the smaller figures (3 and 4) are taken from 

 the fourth cervical vertebra of a Llama. The vertebrae of the Macrauchenia also 

 closely resemble the middle cervical vertebrae of the Vicugna and Llama in their 

 elongated form; approaching the Auchenial division of the Camelidae, and deviat- 

 ing from the true Camels in the relations of the length of the body of the vertebra 

 to its breadth and depth, and in the much smaller size of the inferior processes. 

 Excepting the Giraffe, there is no existing mammal which possesses cervical verte- 

 brae so long as the Macrauchenia ; but the cervical vertebrae of the Giraffe, differ 

 in the situation of the perforations for the vertebral arteries, and in the form of the 

 terminal articular surfaces, as will be presently noticed. 



Both of the cervical vertebrae of the Macrauchenia here described, are of the 

 same size, each measures six inches and a half in extreme length, two inches, 

 ten lines in breadth, and two inches, four lines in depth. In the Giraffe and 

 the Camelidae, the spinous processes are thin laminae of considerable extent in 

 the axis of the vertebra, but rising to a very short distance above the level of 

 the vertebral arch : the spinous processes have the same form in the correspond- 

 ing vertebrae of the Macrauchenia, but present a still greater longitudinal extent ; 

 they commence at the interspace of the anterior oblique processes, and extend to 

 opposite the base of the posterior oblique processes ; the upper margin describing 

 a gentle curve, as shown in fig. 1, PI. VI. The transverse processes also present 

 the form of slightly produced, but longitudinally extended, laminae : their dispo- 

 sition is essentially the same as in the Camelidae, but more nearly corresponds 

 with the modifications presented by the Aucheniae. The inferior transverse pro- 

 cesses, — those which are alone developed in fish, but which are not present in 

 any other vertebrae save the cervical, in mammalia, — these processes in the 

 Macrauchenia are continued from the sides of the under surface of the anterior 

 part of the body of the vertebra ; their extremities being broken off, it cannot 

 be determined how far they extended from the body of the vertebrae, but they 

 gradually subside as they pass backwards : the superior transverse processes are 

 continued outwards from the sides of the posterior part of the body of the vertebra, 

 and gradually subside as they advance forwards along three-fourths of the body 

 of the vertebra : they are not continued into the anterior and inferior transverse 

 processes, as in the Vicugna, but are separated therefrom by a narrow and shallow 

 groove. The articular, or oblique processes, closely resemble those of the Auchenia 



