592 Comparative Morphology of Chordates 



the whale. If "neck" is defined as a constricted region between head 

 and trunk, the whale has no neck, but internal anatomy reveals some 

 cervical features (see Fig. 578). 



The neck, except as traversed by the esophagus and trachea, is a 

 solid region of the animal, consisting mainly of the vertebral column 

 and muscles. Ribs are of chief importance as support for thin walls of a 

 large cavity. In the neck they are very much reduced. In some cases 

 (South American sloths) the last one or two, or even three, cervical 

 vertebrae bear ribs which, however, are shorter than thoracic ribs. 

 Otherwise, cervical ribs appear only as very short embryonic rudi- 

 ments which eventually become solidly fused to the corresponding 

 vertebrae. Like the thoracic ribs, the cervical rib has two protuber- 

 ances or "heads" whereby it is attached to its vertebra. Between the 

 two heads is a space or notch. After the short rib-rudiments have fused 

 to a cervical vertebra, the effect is that of a vertebra having a pair of 

 projecting lateral processes each pierced by a foramen (Fig. 364). 

 Through this vertebrarterial foramen (or foramen transversa- 

 rium) passes an important blood-vessel, the vertebral artery. 



The free mobility of the head depends on an elaborate system of 

 cervical muscles so arranged as to bend the neck in relation to the 

 trunk, to bend the neck within itself, and to give the head a variety of 

 motions in relation to the neck. These muscles are, for the most part, 

 closely massed along the series of cervical vertebrae. The highly com- 

 plex system of muscles constituting the longissimus dorsi of the 

 trunk continues forward into the neck (longissimus cervicis), attach- 

 ing to transverse processes of the cervical vertebrae. A further anterior 

 continuation of it (longissimus capitis) attaches finally to the 

 temporal region of the skull (Fig. 457). 



Action of the dorsal cervical muscles is opposed by muscles having 

 ventral attachment on the cervical vertebrae. The scalenus (Fig. 460) 

 arises from ribs in the lateral thoracic wall and extends forward to 

 attach to transverse processes of the cervical vertebrae. The longus 

 colli (paired) is an important muscle attaching to the ventral surfaces 

 of cervical vertebrae and continuing back along the more anterior 

 thoracic vertebrae. Another ventral muscle, the longus capitis, 

 arises from several cervical vertebrae and inserts on the ventral side of 

 the occipital bones. The shortest vertebral muscles, interspinales, 

 intertransversarii, and transversospinales, occur throughout the 

 neck region just as in the trunk. 



The action of these cervical muscles can be inferred from their 

 attachments. Muscles extending between the thoracic wall and cervi- 

 cal vertebrae bend the neck in relation to the trunk. Muscles whose 

 connections are restricted to the cervical vertebrae bend the neck 



