591 



Comparative Morphology of Chordates 



TAIL 



Comparing mammalian neck and tail with corresponding regions of 

 amphibians and reptiles, it appears that the neck gains importance 

 while the tail loses it. In fishes, aquatic urodeles, and crocodilian rep- 

 tiles, the tail is the chief agency in swimming. Throughout its length, 



OIGAST ANT, 



OMOKYOIDEUS 



STERNOTHYROI0EUS-- ' 



STERNOH^OOEUS-"' 

 TEND RECT ABO-- 

 SCALENUS LONG. . 



STERNOCOST---'" 



INTERCOST EXT...V 



RECTUS ABO 



SERRAT. ANT. 



Fig. 460. Muscles of the head, neck and thorax 

 of the rhesus monkey; left lateral view. The facial 

 and pectoral muscles have been removed. (Cour- 

 tesy, Hartman and Straus: '"Anatomy of the 

 Rhesus Monkey," Baltimore, Williams & Wilkins 

 Co. ) 



nearly or quite to its posterior tip, it conforms to the primitive pattern 

 of segmentally arranged muscles (myomeres), spinal nerves, and 

 vertebrae. In most mammals the tail is extremely attenuated and the 

 characteristic caudal structures are well developed only in its anterior 

 region. Its more important muscles arise from the sacrum and pelvic 

 girdle, extend back for varying distances into the anterior part of the 

 tail, and then break up into slender tendons which attach to the more 

 posterior vertebrae. A posterior region of the tail, varying in extent in 

 different mammals, is quite devoid of muscular tissue and its move- 



