164 THE VOYAGE OF H.M.S. CHALLENGER. 



the ulnar side of the forearm to the radial side of the carpus, and descends as an aponeurotic band 

 of very considerable strength, covering the palmar aspect of the whole of the 1st metacarpal bone, 

 and the radial halves of the 1st and 2nd phalanges of the pollex to the phalangeal cartilage. 

 It passes over the tendons of the thumb, and is inserted into the radial side of the carpus, the 1st 

 metacarpal, and the 1st and 2nd phalanges of the pollex ; into the skin over the radial side of 

 the 2nd phalanx of the pollex ; into the phalangeal cartilage attached to the distal end of the 2nd 

 phalanx of this digit, and it is firmly fixed to the cartilaginous bar, running from the elbow down 

 the radial border of the radius, on the anterior side of the manus to the phalangeal distal cartilage 

 of the 1st digit. Over the middle of the radial side of the 1st metacarpal, the deep palmar tendon 

 gives a strong slip which goes down to the head of the metacarpal and the base of the 1st phalanx. 



The insertion of the longus primus in Otaria and the palmaris longus in Arctoccphalus are 

 alike, so is the insertion of the longus secundus in the former, and the palmaris superficialis in the 

 latter, only the tendon of the superficialis goes down to the 1st phalanx of the 5th digit instead of 

 stopping at the distal end of the 5th metacarpal. The longus tertius in Otaria and the palmaris pro- 

 fundus in Arctoccphalus are not so close ; the latter is much more complicated, its origin being more 

 extensive and the insertion being very different. In Otaria it ends along the radial side of the 1st 

 digit. All are supplied by the median and ulnar nerves. 



The Flexor communis digitorum is a combination representing and built up from — (a) the flexor 

 sublimis digitorum ; (6) the flexor profundus digitorum ; (c) the flexor longus pollicis. 



It arises by three heads, a. The 1st head ' may be regarded as the flexor sublimis digitorum, 

 for it arises from the internal condyle below the palmaris longus (part two), and from the internal 

 lateral ligament, b. The 2nd head 2 resembles the flexor profundus digitorum, for it arises from 

 the inner surface of the ulna posterior to the internal lateral liagment down to 1 inch from 

 the wrist, c. The 3rd head 3 corresponds to the flexor longus -pollicis as it arises from the posterior 

 half of the middle third of the radius below the pronator radii teres, and from the interosseous 

 membrane. The first and third heads are conjoined at the lower third of the forearm, and form 

 one belly ; the second head forms another, and these two bellies unite at the wrist, and thus a broad 

 tendon of considerable strength is formed, which immediately divides into an anterior and posterior 

 set of tendons ; in the anterior set there are three slender ones, in the posterior five stronger. The 

 anterior set is superficial and disposed like the flexor sublimis digitorum ; the posterior is deep, 

 and the first or outermost tendon, like the flexor longus pollicis, goes to the pollex, the remaining 

 four are distributed like the flexor profundus digitorum. Of the superficial set, or flexor sublimis 

 digitorum, the three tendons descend upon the surfaces of the deep tendons for the 2nd, 

 3rd, and 4th digits, opposite the middle of the metacarpal bones ; they enter the sheaths, and 

 over the bases of the 1st phalanges divide to give passage to the deep tendons, and then are 

 attached to the sides and heads of the 1st phalanges of the 2nd, 3rd, and 4th digits. Of the 

 deep set (five), the first tendon or flexor longus pollicis runs along the inner side of the pollex, 

 inside the sheath, and is attached to the head of the last phalanx. From this tendon a smaller one 

 springs, and unites with the sheath of the pollex at the head of the 1st metacarpal bone ; it 

 may be regarded as the only lumbrical. The remaining four tendons or flexor profundus digitorum 



1 Humphry's flexor sublimis digitorum = Lucae's flexor communis digitorum (strongest head). 



2 Humphry's flexor profundus digitorum = Lueae's flexor communis digitorum (second head). 



3 Humphry's flexor profundus digitorum = Lucae's flexor communis digitorum (third head). 



