MUSCULAR SYSTEM OF MAMMALIA. 



19 



fibres are closely attached to the derm, and to the fibrous cap- 

 sules of the roots of the spines. To the circumference of this 

 circular muscle are attached shorter ones at right angles : a pair 

 of these, b, arise from the caudal diapophyses, pass forward and 

 expand to interblend with the posterior periphery : a second 

 pair, d, with attachments to the nasal and premaxillary bones, 

 pass backward over the forehead to the anterior periphery : a 

 third pair, e, arising from the fore part of the sternum, pass for- 

 ward and outward, diverging, and ascending in front of the 

 shoulder to the antero-lateral part of a. A muscle, c, from fascia 

 external to the mandibular angle, ascends between the auditory 

 meatus and the eyeball, and combines with d in operating on the 

 fore part of the great orbicular muscle. 



TVhen the Hedgehog assumes its offensively defensive position 

 it bends and retracts the head and draws forward the pelvis, 

 curving the back, as in fig. 8 : the converging slips b, c, d, e, 

 pull down the orbicular muscle, which relaxes to slip over the 

 projecting parts: the peripheral part, a', #', having descended below 

 these, contracts, and encloses the head, limbs, and body, in an 

 orbicular form. In resuming the normal position the sphincter 

 relaxes, the head is rotated forward, the pelvis and tail are 

 drawn back, the limbs begin 

 to extend themselves: the 

 orbicularis, ', a', is pushed 

 up beyond the meridian, 

 and then contracts, dispos- 

 ing itself, after full exten- 

 sion of the parts beneath, 

 upon the dorsum of the 

 animal, as in fig. 7. Su- 

 perficial sheets of muscle, 

 extending from the shoulder 

 joint backward, s, and over 

 the abdominal region, g, 

 concur with the above-de- 

 scribed in the motions of 

 rolling and unrolling the 

 animal. One of the lateral 

 muscles of the snout is 

 shown at m, the masseter 

 at c. 



In the order Bruta the most notable modifications of the mus- 

 cular system are met with in the Anteaters. 



c 2 



8 



Orbicularis dermal muscle, Hedgehog, half unrolled. 



XLIII. 



