320 ELEMENTARY ANATOMY. [LESS. 



be excessive in mass, as in most Fishes, or in complexity, as 

 in Serpents. 



The trapezius is a very constant muscle, but may be much 

 more restricted or more extended in its origin than is the 

 case in man. It may also be divided into two portions, as 

 notably in the Mole, where the two origins are very wide 

 apart : (i) the occiput, and (2) the first two lumbar ver- 

 tebrae. It may be very small, as in Menobranchus (Fig. 286) ; 

 or may unite with the latissimus dorsi, as in Anguis fragilis; 

 or with part of the deltoid, so as to go directly to the humerus, 

 as in some Mammals without clavicles. 



In Bats a long slender segment of this muscle may pass 

 along the upper margin of the wing membrane from the 

 occiput to the distal phalanx of the pollex. 



In the Flying Squirrel Pteromys a similar muscular band 

 goes to the rudimentary pollex, but it springs from the zy- 

 goma, and is therefore rather a modification of the platysma 

 myoides than of the trapezius ; as it is also in Galeopithecus. 



739 



FIG. 289. MUSCLES OF THE VENTRAL ASPECT OF THE BREAST AND LEFT 

 WING OF AN EAGLE (Aquilajucosti). 



(After A. Milne- Edwards.} 



i, pectoralis major, sending out a slip, 2 (as the tensor petagii longus) to the first 

 metacarpal ; 3, tensor petagii brevis ; 4, biceps ; 5, triceps ; 6, brachialis 

 anticus ; 7, pronator brevis ; 8, pronator longus; 9, flexor carpi ulnaris ; 10, 

 extensor metacarpi radialis longus ; n, extensor carpi radialis ; 12, abductor 

 pollicis ; 13, points just above a long tendon of the flexor profundus ; 14, flexor 

 brevis digitorum. 



In Birds an analogous and similarly slender muscle goes 

 to the pollex or to a sesamoid at its base, but this muscle 

 is often an offshoot from the pectoralis major, though it may 

 contain fibres from the deltoid or from the biceps showing 

 in what diverse ways a similar want may be supplied. 



The ligamentum nuchce of man is but a rudiment of that 

 vast band, or sheet, of fibres which in many animals (e.g. the 



