CHAP, v.] THE CAT'S MUSCLES. 153 



one on the ulnar ^ side of the fourth digit. "When the palmar 

 surface of the paw is looked at, a double interosseus is to be seen on 

 the ulnar side of the index ; one is also to. be seen on the radial side 

 of the fifth digit, and we also see those which were partly visible 

 when the paw was viewed dorsally. We thus learn that those seen 

 dorsally on either side of the third digit have a common belly on 

 the palmar surface, as also that the dorsal interosseus, which appears 

 on the ulnar side of the fourth digit, has a palmar division going 

 to the radial side of the fourth digit. In this way each digit (apart 

 from the pollex) has a pair of interossei, except the fifth digit, which 

 only has an interosseus muscle on its radial side. 



These little muscles act mainly as short flexors, but also somewhat 

 as extensors. Each is a double-bellied muscle which divides, and 

 is doubly inserted : one insertion being into the first phalanx and 

 sesamoid beneath it, and the other extending upwards towards the 

 sheath of the extensor tendons, and so helping to retract the claws. 



The muscles of the anterior region of the trunk, and of the fore- 

 limbs, are invested by a membrane called the superficial fascia, and a 

 synovial membrane is placed in the subcutaneous tissue which 

 invests the acromion, olecranon, and joints of the paw. 



A deeper, stronger fascia is placed in the axilla, which descends 

 the arm and becomes continuous with the annular ligaments of the 

 wrist, beneath which pass the flexor and extensor tendons, their 

 passage being facilitated by the presence of synovial membranes. 



The strong palmar fascia, in which the palmaris longus ends, has 

 already been mentioned. 



As to the STRETCH OF MUSCLES over the segments of the pectoral 

 limb, we have seen that some muscles which are inserted into the 

 shoulder- girdle proceed from the trunk, as the trapezius; others pro- 

 ceed from the shoulder- girdle to the upper arm, as the deltoid; others 

 from the upper- arm to the fore- arm, as the brachialis anticus ; and, 

 finally, others from the fore-arm to the hand, as the deep flexors 

 of the digits. But there are also muscles which pass direct from the 

 trunk to the upper-arm, as the latissimus dorsi ; or direct from the 

 shoulder to the fore-arm, as the biceps ; or direct from the upper- 

 arm to the hand, as do a great number of the muscles inserteot into 

 the latter the flexores, carpi radialis and ulnaris and the flexor sub- 

 limis digitorum, arising, as we have seen, from the inner, or ulnar, 

 condyle of the humerus ; and the extensores carpi radialis longior 

 et brevior, the extensor communis digitorum and extensor carpi 

 ulnaris, arising, on the contrary, from its outer, or radial, condyle. 

 The extensors, as well as the flexors of the digits, all take origin 

 in the arm and not in the hand itself. 



As to the DIRECTION of the muscles of the arm the long flexors of 

 the pollex and other digits are not oblique, but arise on the same 

 side of the limb as that on which they are distributed. 



The extensors of the outer digits cross the extensors of the thumb. 



As to the NUMBER OF MUSCLES WHICH MAY BE INSERTED INTO A 



SINGLE DIGIT, we see that the ideal perfection of having both a flexor 



