554 mr. j. beswick-perrin on the [June 20, 



the first phalanx of the fifth digit. There is a small sesamoid bone 

 developed in the tendon of origin of the latter muscle. 

 The muscles of the pollex are three in number : — 



1 . Abductor pollicis, which takes its origin from the radial sesa- 

 moid bone and the os trapezium. It is inserted into the radial side 

 of the base of the first phalanx and its sesamoid bone. 



2. The opponens pollicis arises from the trapezium. It is inserted 

 into the distal part of the pollex metacarpal, and into the sesamoid 

 bone on the radial side of the metacarpo-phalangeal articulation. 



3. Flexor brevis pollicis consists of two portions: one arises from 

 the trapezium, and is inserted into the sesamoid bone and base of first 

 phalanx ; the other arises from the trapezoid and os magnum, and 

 is inserted into the ulnar side of the base of the pollex proximal pha- 

 lanx without impinging on the sesamoid bone. 



The pronator quadratus occupies almost the entire length between 

 the two bones of the forearm. 



The interossei of the fore foot. There are only two superficial 

 palmar interossei. They arise together by a thin flat tendon from 

 the os magnum. Directly after their origin they diverge from each 

 other: the one on the radial side terminates at the base of the first 

 phalanx of the second digit on its ulnar side ; the other (or ulnar 

 side one) goes to the radial side of the base of the first phalanx of 

 the fifth digit : the first abducts the index digit from the pollex ; the 

 second adducts the fifth digit in the direction of the pollex. In the 

 words of human myologists, both adduct towards a line drawn down 

 the centre of either the third or fourth digit. The deep interossei 

 are six in number : the first arises from the pollex and index meta- 

 carpal bases and shafts, the second and third from the interval 

 between the second and third metacarpals ; the fourth and fifth 

 between the third and fourth, and the sixth between the fourth and 

 fifth metacarpals. They are inserted as follows : — Each of the second, 

 third, and fourth digits receives one on each side. There are two 

 sesamoid bones in connexion with each metacarpo-phalangeal articu- 

 lation ; and these muscles are connected respectively with each of 

 them, and thus prolonged to the sides and bases of the proximal 

 phalanges. 



The first, third, and fifth adduct the second, third, and fourth 

 digits towards the pollex ; the second, fourth, and sixth abduct them 

 from the pollex. These muscles can scarcely be called interossei ; 

 they are situated in a great measure upon the metacarpals rather 

 than between them. The superficial ones are altogether removed 

 from contact with the metacarpals. A good name for the deep 

 layer would be " bilateral flexors." Any two of these muscles acting 

 conjointly would produce direct flexion of the first phalanx on to the 

 metacarpal. This is probably their true use in the living subject. 



The Extensors of the Fore Limb. 



The supinator longus, the extensor carpi radialis longior and 

 brevior are exactly the same as in the human subject. In the 



