158 DR. J. MURIE ON THE FORM AND STRUCTURE OF THE MANATEE. 
the arm towards the chest is mainly effected through the upper attachment ; but increased 
leverage is gained by means of the more distant fascial fixed point. The continuation 
into the forearm is by a strong aponeurosis, which stretches in a bridge-like manner from 
the humeral tendon over the bend of the elbow, and is fastened to the neck of the radius 
at its tuberosity. 
The pronator radii teres shoots obliquely over this radial insertion ; and the diminu- 
tive tendon or second portion of the biceps joins and terminates along with it. On 
its outer surface the aponeurosis in question is covered by and adherent to the flesh of 
the brachialis anticus. The thick cord of the rete mirabile and the brachial nerves are 
lodged securely, and pass downwards beneath the aforesaid aponeurotic bridge ; for as 
extension of the forearm occurs the expanse of fascia is rendered tense, and thus 
prevents undue pressure or strain upon the vessels beneath. 
(B) Those of the Pectoral Limb. Dorsal=Extensors.—As respects the triceps, 
the long scapular head is fleshy, its origin extending for one and a half inch from 
the capsular ligament, to which it is firmly attached. The middle head arises the 
whole length of the back of the neck of the humerus, and has a flat broad belly. 
The short head occupies the whole of the back of the shaft of the bone; above 
it is narrowest, and inclines obliquely inwards. The three heads, as usual, unite 
below, and proceed to a short flat tendon to the olecranon process. 
No anconeus was observed. 
The obliquely triangular elevator and retractor of the humerus, the de/toid, is of con- 
siderable size and moderate thickness. Its fibres are not very coarse or disposed in 
protuberant bundles as obtains in Man. Origin, the whole length of the short spine 
of the scapula, its lower border; and it is firmly fixed to the loose acromial cartilage. 
From this last point its fibres trend downwards, those behind slanting forwards, 
the front of the humerus projecting beyond its anterior edge The muscle bifurcates 
slightly above the middle of the humerus, at the position of the here absent deltoid 
eminence; the insertions, each tendinous, embrace the biceps, and are fixed to about 
the middle of the shaft; but the posterior portion continues towards the elbow. 
The supinator longus is fair-sized. Origin, humerus above outer condyle, close to 
the brachialis anticus. It runs along the outside of the radial shaft, and round the 
styloid process, being inserted into the trapezium. It is tendinous where passing along 
the radial groove, and at insertion spreads out aponeurotically. If a supinator brevis 
obtains, it is with difficulty separated from the brachialis anticus; muscular fibres 
apparently continuous with the latter cover the orbicular ligament and neighbourhood 
a little downwards. 
Extensores carpi radiales longior and brevior appear to be represented by a single 
muscle with a condylar origin, a flat belly continuing three fourths the length of the 
radius. The distal tenaon, also flat, lies in the middle radial groove and widens out 
over the carpus, being fastened into the proximal ends of the second and third digits, 
