3 28 ELEMENTARY ANATOMY. [LESS. 



Triceps. The great extensor of the arm in man, in spite of 

 its size and complexity, is small and simple compared with 

 conditions which may obtain. Thus it may (as in Hyrax) 

 have four heads, and in addition a fasciculus going from the 

 surface of the infra-spinatus to the olecranon, and called 

 the dorso-epitrochlear (Fig. 295, Zte.) It may be very powerful 





FIG. 295. MUSCLES OF OUTER SIDE OF FORE-LIMB OF HYRAX. 



m, serratus magnus ; Re, rhomboideus capitis ; Ssfi, supra-spinatus ; Isp, 

 infra-spinatus ; D, deltoid ; Tmaj, teres major : De, dorso-epitrochlear ; 

 jT 1 4, triceps ; Ba, brachialis anticus ; SI, supinator longus ; Eld, extensor 

 longus digitorum ; Emd, extensor minimi digiti. 



and take origin largely from the scapula, as in the Pig and 

 Echidna, or it may take origin from the coracoid also, as in 

 the Iguana. It may be quite rudimentary, as in the Porpoise. 

 21. The MUSCLES OF THE FORE-ARM in man attain almost 

 their maximum of complexity. As might be expected, they 

 become greatly reduced in animals the hands of which have 

 little mobility (as Birds and Cetaceans) or have a reduced 

 number of digits. In Birds the actions of the pronators and 

 supinators are modified and limited to opening and shutting 

 the wing, i.e. to ad- and ab-duction. 



