36 



ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 



nearly entire, the proximal and distal extremities of the left tibia and fibula ; 

 and a metatarsal bone of the left hind foot. 



Before entering upon the description of these remains, a few observations 

 may be advantageously premised on some of the distinguishing characters of the 

 Camelidse. It is well known that the Camels and Llamas deviate in their denti- 

 tion, viz., in the presence of two incisors in the upper jaw, from the true Ruminants; 

 and we cannot avoid perceiving that in this particular the direction in which they 

 deviate tends towards the conterminous Ungulate Order, in which incisor teeth 

 are rarely absent in the upper jaw. They also further deviate from the Ruminants 

 and approach the Pachyderms in the absence of cotyledons in the uterus and 

 fetal membranes ; having, instead thereof, a diffused vascular villosity of the 

 chorion, as in the sow and mare. 



But besides these characters, by which, in receding from one type of hoofed 

 mammalia, the Camelidse claim affinity with another, there are many parts of their 

 organization peculiar to themselves ; of some of these peculiarities, the relation to 

 the circumstances under which the animal exists, can be satisfactorily traced ; 

 in others, the connection of the structure with the exigencies of the species, is by no 

 means obvious, and in this predicament stands the osteological peculiarity, which 

 is immediately connected with our present subject — a peculiarity in which the 

 Camelidse differ not only from the other Ruminants, but from all other existing 

 Mammalia, and which consists in the absence of perforations for the vertebral 

 arteries in the transverse processes of the cervical vertebrae, the altas excepted. 



I may observe that what is described as a perforation of a single transverse 

 process in a cervical vertebra is essentially a space intervening between two 

 transverse processes, a rudimental rib, and the body of the vertebra. In the cold- 

 blooded Saurians,— in which the confluence of the separate elements of a vertebra 

 takes place tardily and imperfectly, if at all,— the nature of the so called perfora- 

 tion of the transverse process is very clearly manifested, as in the cervical verte- 

 brae of the Crocodile, in which the interspace of the inferior and superior trans- 

 verse processes is closed externally by a separate short moveable cervical rib. 

 In the Ornithorhynchus paradoxus the vertebra dentata also preserves through- 

 out life this condition of its lateral appendages : in other Mammalia it is only in 

 the foetal state that the two transverse processes are manifested on each side with 

 their extremities united by a distinct cartilage, which afterwards becomes ossified 



and anchylosed to them. 



In the Hippopotamus the inferior transverse process sends downwards a 

 broad flat plate extended nearly in the axis of the neck, but so obliquely, that the 

 posterior margins of these processes, in one vertebra, overlap the anterior ones of 

 the succeeding vertebra below, like the cervical ribs in the Crocodile ; the same 

 structure obtains in many other mammalia, especially in the Marsupials. In the 



