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



surface of the radius, to the outer side of the extensors of the pollex, at the junction of the epiphysis 

 with the shaft. In Trichechus it is single, and arises from the deltoid ridge and shaft of the 

 humerus. In Otaria it is double headed ; the external head comes from the upper end 

 of the external condyloid ridge and the internal from the deltoid ridge and joins the external 

 head. 



Vrolik, under Section 23, describes the Extensor ossis metacarpi pollicis as the supinator longus. 

 Humphry describes it as inserted into the projecting margin of the radius and Lucae the same ; Dr. 

 Murie in Otaria into the outer side of the styloid process, and in Trichechus to the styloid process. 

 It appears to me that these authors have not sufficiently defined the exact place of attachment to 

 the radius. In the Phocinfe and Arctoccphalus there is only one groove for the tendons to the 

 thumb. In the former it is placed obliquely downwards and inwards across the anterior border of 

 the radius ; in the latter it runs down on the outer side of the anterior border ; one-quarter of the 

 groove in both is on the epiphysis. In the Phocinfe the supinator is inserted into the anterior 

 border of the radius above the groove, and the same in Arctoccphalus. It flexes the forearm, and 

 supinates it when prone. It is supplied by the musculo-spiral nerve. 



The Extensor carpi radialis arises from the external supracondyloid ridge, lies to the outer side 

 of the supinator longus, and passes along the anterior border of the radius ; above the wrist it passes 

 below the tendon of the extensor ossis metacarpi pollicis, and then through the second division of the 

 annular ligament ; above the carpus it divides into three tendons. The outermost is inserted into the 

 base of the radial side of the 1st metacarpal bone, the middle into the dorsal surface of the radial 

 side of the scapholunar, and the innermost into the radial side of the base of the 2nd metacarpal bone. 



In Phoca barbata there is a variation ; half an inch above the extensor ossis metacarpi 

 pollicis it divides into two tendons. The outer is inserted into the base of the 2nd metacarpal 

 bone. The inner gives off from its outer side a slip, which goes to the dorsum of the trapezium, 

 and then is inserted into the outer side of the 2nd metacarpal bone. 



In Arctoccphalus it lies to the outer side of the supinator longus above the elbow. It arises 

 from the external condyle as in the Phocinfe, below where the musculo-spiral nerve turns round the 

 external border of the humerus, slightly from the anterior surface of the capsule of the joint over 

 the head of the radius, and from the external condyle. In the forearm it has the same relations 

 as in the Phocinfe. Before passing beneath the extensors of the pollex, it divides into two tendons of 

 equal size. The anterior or outer tendon is inserted into the "ulnar side of the base of the 1st 

 metacarpal. The posterior or inner into the upper third of the radial side of the base of the 

 2nd metacarpal. Vrolik, under Section 24, says of the extensor carpi radialis longus and 

 brevis that both rise from the upper part of the outer margin of the humerus. The brevis is inserted 

 into the lower part of the radius, and the longus into the outer face of the os navicularis. From 

 the insertions the short one is the supinator and the long the extensor carpi radialis. 



Humphry and Lucae describe two metacarpal insertions. Otaria has the longus and brevis 

 as a common mass with two tendons. The insertions are similar to those in Arctoccphalus. In 

 Trichechus they are so united that they cannot be distinguished. The insertion is by a single tendon 

 attached equally to the 1st and 2nd metacarpals. In Phoca larbata the muscle forms two tendons 

 about the middle of the radius, in the other PhocinEe it is divided equally in the region of the carpus 

 into three, and in Arctoccphalus into two as in Phoca barbata. There is therefore an attempt to form 

 two muscles in Phoca barbata and Arctoccphalus, but as the origins in all the Phocinfe are from the 



