The most important muscles of the humerus are the pectoralis major, the latissimus dorsi, and the tcrcs major, all of which are of great size ; and it is by means of these muscles that the astonishing efforts of the animal are made in excavating his passages, and throwing the earth behind him. The pectoralis major is of extraordinary thickness. It is formed of six portions, which arc all of them inserted into the broad quadrate portion of the humerus. Four of these portions arise from the sternum, the fifth from the clavicle ; and the sixth passes across transversely from one arm to the other. The latissimus dorsi is also of considerable size, and is inserted into the posterior surface of the quadrate portion of the humerus. The trres major, which is of enormous thickness, is in serted near the former muscle.
The other muscles of the anterior extremity do not require particular description.
There is one peculiarity in the muscular sys tem which deserves special notice; it is the enormous development of the panniculus car nosns in the hedgehog, by which it is enabled to roll itself up in a ball with such astonishing force as to afford with its spiny covering a complete protection against its most powerful antagonists. I proceed to describe this ap paratus and its uses.
As this muscular apparatus has no attach ment but to the skin, it changes its position with every movement of the integument ; and it is therefore necessary to consider it under the various relations which it assumes in the different positions of the animal. Considering it then, in the first place, as rolled up in a ball (fig. 447), either for defence or during repose, the whole body is enveloped beneath the skin by a strong sac or covering, consisting of a mass of fleshy and concentric muscular fibres, of an oval form. All these fibres are attached intimately to the skin, and even to the base of the spineswith which it is every where furnished, so that it is even difficult to detach the fibres in dissection. The thickest part of this fleshy sac is at the lower margin or mouth of the sac, at which part it forms a sort of sphincter, com posed of orbicular muscular fibres. On the other hand, when the hedge-hog is unrolled, and at its full length (fig. 448), the muscle in question totally changes its figure and relations. The muscle now lies over the back, forming an oval covering, the middle of which is very thin, and the circumferenee exeeedingly thick and somewhat raised. To different portions of this circumference of the muscular covering are attached several accessory muscles. Anteriorly there are two pairs; one arising from the me dian line and inserted into the nasal bone ; the other, more external, apparently confounded at its origin with the external orbicular fibres, is inserted into the side of the nose and incisive bones. Posteriorly a pair of broad muscles, of a pyramidal form, arise from the posterior part of the fleshy circumference, and are in serted into the side of the tail towards the ex tremity.
On the ventral aspect there arc also several portions of muscle, belonging to the same ap paratus. There is one beneath the throat, aris ing from the anterior part of the thorax, under the skin, and is inserted about the lateral parts of the head near the ears. Another arises from
the median line of the sternum, and passes obliquely forwards over the shoulders, in front of them, to join the margin of the great or bicular muscle before described. There is another ventral portion which has a very ex tended connexion. It is attached around the anus, to the lateral parts of the tail and neigh bouring parts, extends over the whole surface of the abdomen, and then divides into two portions; one internal, and larger than the other, passes under the axilla, and is inserted into the superior and interior part of the humerus; the other, external, passes laterally upwards, be inserted into the margin of the great or bicular muscle near the neck. The muscles hitherto described lie superficially; but there are others which are seated underneath the great muscle of the back. One arises from the side of the head, being attached to the meatus auditorius on each side, and loses itself in the anterior point of the orbicular muscle. There is also a thin layer of fibres lying beneath the great muscle, of which the anterior are attached to the superior interior portion of the humerus, and the pogterior to the third ventral muscle already mentioned.
We have here a very extensive and a very powerful apparatus, and it now becomes ne cessary to consider its application. When the hedgehog is rolled up in a ball, it is com pletely enveloped, as regards all the upper and Literal parts of the body, in the great orbicular muscle. When once brought into this position the simple contraction of the thick circum ference of the muscle, which forms a true sphincter, is suflieient to retain it. If the ani mal unrolls itself, the disc of the great muscle contracts whilst the circumference is relaxed, allowing the exit of the feet and the uncover ing of the belly and sides: then the whole muscle contracts together, and lies in a mass on the hack. By this universal contraction, the necessary muscles become stretched, and in a condition to perform their several offices ; by the contraction of the anterior ones the head, and by that of the posterior the tail, is raised, whilst those which lie beneath raise the head and neck together, and animal is now ready fur progression. On the other hand, on the apprehension of danger, or when reposing, it rolls itself into a ball by the following pro cess. The orbicular muscle relaxes, and the muscles extending from it to the head and to the tail extend it in those directions, whilst the deap-seated transverse muscles which are at tached to the external lateral portions, and lie on the belly, bring this part of the circum ference downwards. At the same time the head is brought downwards towards the breast by the ordinary flexion of the head, and by the cutaneous muscles of the neck already de scribed; the tail and the hinder legs are brought forwards under the belly, and the flexors of the limbs contract. The great orbicular muscle passes downwards over the sides, then contracts at the circumference, and forms a sort of sac or purse, enveloping the whole body and limbs.