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



deltoid. These muscles for rotating the humerus have more leverage by being removed from the 

 shaft by a vertical plate. 



The brachialis anticus muscle in the Phocinse is single, and divides into two for insertion into 

 the radius and ulna. Lucae gives the division for the ulna as in combination with the biceps, but 

 Humphry and I find it quite apart. In Otaria as in Arctoccphalus it has two heads of origin, 

 but in the former the outer head joins the inner head on the outer side of the elbow, whereas 

 in Arctoccphalus the head from the surface of the deltoid eminence divides into two, one going to 

 each bone of the forearm, and the outer has also two divisions for both bones. In the Phocinfe 

 it is supplied by the musculo-cutaneous and musculo-spiral. In Arctoccphahis it is supplied by 

 the musculo-cutaneous. It is a flexor of the forearm on the upper, and, like the biceps, will 

 rotate the forearm outwards when the manus is prone. 



The Posterior Brachial Region in the Phocina? and Arctocephali consists of the triceps, which 

 has four heads — (a) the dorsi-epitrochlear, (b) the long head, (c) external licad, and (cl) internal head. 

 There is no subanconeus. 



The Triceps, first head, or the dorsi-epitrochlear, 1 is a thin muscle partially covered by the deltoid, 

 and arises from the dorsum of the scapula by a broad sheet-like tendon, extending from the vertebral 

 border of the cartilaginous plate to a spot posterior to and in a line with the middle of the scapular 

 spine. This tendon is continuous with the tendon of origin of the long head of the triceps, and it is 

 placed between the origin of the infraspinatus anteriorly and the teres major posteriorly. Above 

 the olecranon of the ulna it collects into a small muscular band, which runs over the border of the 

 olecranon, near its junction with the posterior border on the internal surface of the ulna. After 

 receiving a few fibres from the long head it is inserted, or rather moored by its lower edge, to the 

 junction of the olecranon with the posterior border of the ulna, and to one inch of the posterior 

 border below this junction. The band passes to the flexor minimi digiti, blends with it, and 

 terminates at the junction of the middle and upper third of this muscle. In Phoca barbata the 

 insertion overlapped both sides of the olecranon. 



In Arctoccphalus gazella it is of a triangular shape, and arises from the dorsal rim of the inferior 

 costa of the scapula, by a sheet-like tendon which is one inch long, and extends transversely from the 

 posterior angle to the middle of the dorsal rim of the posterior costa of the scapula. It is placed 

 between the infraspinatus anteriorly, and the teres major and subscapularis posteriorly. It becomes 

 cylindrical over the olecranon, slightly overrides both sides of it, and there receives a few fibres from 

 the external head on its outer side, and is inserted into the olecranon from the middle tubercle to 

 the posterior, and into the posterior and outer upper third of the flexor carpi ulnaris. 



The difference in this muscle in Phoca vitulina and Ardocephalus according to my dissections is 

 well marked. In the former the origin is far removed from the axillary border by the extensive 

 surface for the origin of the teres major, which in the latter is adjacent to this border. The insertion 

 in Phoca blends with the flexor minimi digiti, and in Arctoccphalus with the flexor carpi ulnaris. 



The statement by Professor Humphry that the muscle reaches the paddle finds no support 

 from Lucae, and in none of the specimens did I see this ; perhaps the flexor minimi digiti was 

 included with it in his description. Lucae gives its insertion into the fascia of the front arm, &c, 



1 This is Humphry's first division ; Lucae {op. cit, pi. ix. fig. 1) calls it the " triceps pars longa," and in his text 

 " portio longa tricipitis." 



