208 ANATOMY OF THE HEAD. 



to those of the other parts of the body. Upon the crest, or 

 upper margin of the neck, is a line of flowing hair, called 

 the mane ; and on the top of the forehead is a tuft of hair 

 termed the forelock. 



The cervical ligament, or ligamentum nuch(B (see Fig 14), 

 is a very strong, partly ropelike and partly an expanded or 

 a clothlike substance ; which is principally placed be- 

 tween the head and the body, as a support to the head ; 

 but extends all along the dorsal spines, even to the com- 

 mencement of the tail. The muscles of the neck are very 

 strong : but muscles, if constantly kept in action, tire ; 

 Nature has, therefore, given a yellow elastic fibrous sub- 

 stance, to support the weight of the head, and take the 

 stress from the muscular fibre, but permit of the freest 

 motions of the head. It is strongly attached, by its anterior 

 extremity ; to the posterior part of the occipital bone ; 

 passing over the first cervical vertebra, without attaching 

 itself to it, but being intimately connected with the spinous 

 processes of all the rest. The muscles of the neck operate 

 on the head ; and many of the fleshy masses moving the 

 neck, originate on the shoulders. 



The trachea, or windpipe {Plate VI. /), is a large canal 

 which arises from the cricoid cartilage of the larynx, and 

 extends down the anterior part of the neck into the thorax : 

 it is composed of upwards of fifty annular cartilages, which 

 taper from their front, terminating in mere slips ; having 

 at their extremities a strong muscular band, which unites 

 their substance in the form of numerous circles, but does 

 not fix tlieir form or position. This muscle extends the 

 whole length of the trachea, and is present on every part of 

 the cartilages ; only it becomes very thin, and somewhat 

 difficult to detect upon the anterior portion of the tube. 

 The numerous cartilaginous rings forming the trachea are 

 connected at their edges to each other by strong elastic 

 ligaments : thus rendering the trachea perfectly flexible. 

 Externally it is united to the surrounding parts by cellular 

 substance ; internally it is lined by a mucous membrane, 

 the secretion of which defends it against the irritating effects 

 of varieties in the temperature. About the third or fourth 

 dorsal vertebra, it divides into two branches or bronchiee ; 

 the principal di\'isions of which again divide, before they 



