444 THE ANATOMY OF VERTEBEATED ANIMALS. 



centrale in the carpus, so that it has nine bones. The 

 scaphoid and lunare are ankylosed, as in the Carnivora, and 

 the pisiform bone is much elongated. The pollex and the 

 fifth digit are the shortest. 



The pelvis is remarkably spacious. The symphysial 

 union of the pubes is always small, and, sometimes, the 

 bones remain separate. The subpubic arch is much rounded. 

 The ilium is narrow, and a mere ridge separates the iliac 

 fossa from the gluteal surface. The femur has a round 

 ligament, and a prominent ridge represents a third tro- 

 chanter. The distal ends of the tibia and fibula are anky- 

 losed together. 



One of the most notable peculiarities of the Hedgehog 

 is its power of rolling itseH up into a ball, from all sides of 

 which the spines protrude. This is effected, for the most 

 part, by the contraction of the greatly developed cutaneous 

 muscle, the chief fibres of which are disposed as follows. A 

 very broad band, the orbicularis pannic^di, encircles the body 

 laterally. In front, it, partly, arises from the nasal and 

 frontal bones, and, partly, is the continuation of a thick 

 mass of fibres which pass over the occiput. Posteriorly, 

 each lateral division of the muscle spreads out into a very 

 broad band, which is thick ventraUy and thin dorsally, and 

 adheres closely to the skin, from the line at which the hairy 

 and spinigerous surfaces join, to near the median line of 

 the back. Posteriorly, the two lateral halves of the orbi- 

 cular muscle pass into one another upon the distal haK of 

 the short tail. 



The action of this muscle will depend upon the attitude 

 of the animal when it contracts. If the head and tail are 

 fully extended, the orbicularis can only diminish the dimen- 

 sions of the spinigerous region of the skin and erect the 

 spines. But if the head and tail be more or less flexed, as 

 they always are in the ordinary attitude of the Hedgehog, 

 the orbicularis will play the part of a powerful sphincter, 

 approximating the edges of the spinigerous area towards 

 the centre of the ventral side of the body, and forcibly 

 enfolding the trunk and limbs within the bag thus formed; 



