112 MORPHOLOGY OF THE ORGANS OF VERTEBRATES. 



tissue wanders in among the separate muscle cells, forms an 

 envelope (perimysium), and binds these together into bundles, 

 and bundles into muscles. This perimysium, which extends 

 beyond the contractile or true muscular portions, also forms 

 the means of attachment l of the muscles to the parts which 

 are to be moved ; it gives rise to what are known as ten- 

 dons, sometimes, as in the extremities, of considerable length. 

 Tendons may occur not only at the ends, but in the middle 

 of muscular tracts. When forming broad, flat sheets, tendons 



my v gl o f g t 



FIG. 122. Anterior end of embryo dogfish, Acanthias, viewed as a trans- 

 parent object, a, anterior head cavity; b, first true gill cleft; e, eye; f, facial 

 nerve ; f(>, fore brain ; g, Gasserian ganglion ; gl, glossopharyngeal nerve ; h, heart ; 

 m, position of mouth; nib, mid brain; my, myotome ; o, auditory capsule; /, 

 pinealis ; s, spiracular cleft; /, trigeminal nerve; v, vagus nerve; I, 2, first and 

 second head cavities of van Wijhe. 



are called fascia or aponeuroses. Frequently ossification may 

 occur in tendons, familiar examples being found in the patella 

 or knee-pan of man, the bony tendons in the ' drumstick ' of 

 many birds (turkeys), etc. 



In shape the muscles vary extremely. In the trunk region, 

 as a rule, they are short and more or less flattened ; in the ex- 

 tremities they are usually prismatic or cylindrical, and greatly 

 elongate. They may have one or several heads ' or points of 



1 That attachment of a muscle which usually remains without motion in the contrac- 

 tion of a muscle is spoken of as its origin ; the attachment to a movable portion as its 

 insertion. 



