VIII.] 



THE MUSCLES. 



Mammals, e.g. Talpa and Spalax; and in Lepidosiren, the 

 Lamprey, and Lancelet amongst Fishes. 



On the contrary, muscles may be developed which do 

 not exist in man at all. 



Thus in most Mammals (e.g. the Horse) a conical funnel- 

 shaped muscular mass may spring from around the optic 

 foramen, and, passing within the recti, attach itself to the 

 sclerotic. 



FIG. 283. DEEPER MUSCLES OF RIGHT SIDE OF MENOPOMA (the mylo-hyoids 

 and trapezius being removed or cut short). 



AA, adductor arcuum ; CA, constrictor arcuum ; CF, constrictor faucium ; CHE, 

 cerato-hyoideus externus ; CHI, cerato-hyoideus interus ; D, deltoid ; Z>' and 

 1) 2 , digastric; ExO, external oblique; G ff, genio-hyoideus; InO, internal 

 oblique ; LAS, levator anguli scapulae ; LD, latissimus dorsi ; M, masseter ; 

 S, subclavius ; SM, serratus magnus ; T, trapezius. 



This mass may divide itself into two portions, as in the 

 Rhinoceros ; three, as in the Frog ; or into four, as in the 

 Porpoise. In the last case we have thus four supplementary 

 recti muscles within the four normal ones. 



It may be that the superior oblique muscle does not pass 

 through a pulley. It does not do so in Vertebrates below 

 Mammals, where it arises at the front part, not the back of 

 the orbit. 



The two oblique muscles may thus arise, one above the 

 other, from the inner angle of the orbit, as in the Frog and 

 in Fishes. 



The muscles of the eye may take origin in part from the 

 basis cranii and in part from the fronto-parietal, as in the Frog ; 

 or they may spring from within a bony canal situated beneath 

 the basis cranii, as in many bony Fishes, e.g. the Carp. 



