SKELETON OF INSECTIVORA. 385 



cliute to support this light and delicate species of Rodent, 

 fig. 154, in its long flight-like leaps from bough to bough. In- 

 creased stiffness and resistance are imparted to the bones of 

 the arm by the anchylosis of the radius, 54, and ulna, 55, at 

 their distal halves. The tibia, 66, and fibula, 67, are similarly 

 united. 



There are few generalisations deducible from the limb-bones of 

 Rodentia. The absence of clavicles accords, in the main, with 

 natural groups ; but Lagomys is an exception among LeporidcB 

 and Chinchilla among Hi/stricidce, Wth. : most non-cla\dculate 

 Kodents have the tibia and fibula distinct. 



Among the bones of the splanchnoskeleton may be noted the 

 ^ OS penis,' which is present in most members of the Kodent 

 order. 



§ 182. Skeleton of Insectivora. — The present like the preceding 

 Lissencephalous order has species organised, not only, as in 

 Hedgehogs, for ordinary terrestrial progression, but also for leap- 

 ing and swimming, and in a more especial degree for burrowing 

 and flying. 



A. Vertebral Column. — In the Hedgehog the vertebral for- 

 mula is: — 7 cervical, 15 dorsal, 6 lumbar, 3 sacral (or L 5, s 4), 

 and 14 caudal. The transverse processes of the last cervical are 

 not perforated. All the processes are small throughout the verte- 

 bral column, and ofler no impediment to the free inflection of the 

 spine required in the defensive array of the prickly integument. 

 The sacrum is narrow and articulates by three vertebra with the 

 ilia: these form an angle of 130° with the spinal column : the 

 ilio-pubic angle is about 150°: the symphysis is short and the 

 pelvic outlet large. The neural canal is widest in the cervical 

 region, contracts towards the middle of the back, and expands a 

 little in the loins. Seven pairs of ribs directly join, by hasma- 

 pophyses often ossified, the sternum, which consists of four bones. 

 The cancellous structure of the vertebra? is light and open. 



The Tenrecs {Centetes) have 19 dorsals with 5 lumbar ver- 

 tebrae, and the neural spines are longer on the anterior ones and 

 the contiguous cervical vertebrae, in relation to the larger skull 

 and more powerful jaws of these tropical Hedgehogs. 



In the leaping Macroscelides, with d IZ, I 1 , the neural spines 

 of the hinder dorsal and lumbar vertebra? are longer, and, with 

 those anterior to them, indicate '^ a centre of motion' of the trunk. 

 The caudal vertebrae are more numerous and have hjemapophyses 

 in part of the series. This part of the skeleton is also Avell deve- 

 loped in the climbing Tupaias. 



VOL. II. c c 



