MYOLOGY 95 



Relations. Infero-anteriorly with the anus. Posteriorly with the 

 edges of the ilium and of the ischium. Internally with the depressor 

 caudae. 



Action. Gives support to the viscera in the post-anal regleH^ 

 and aids in attaching the anus to the structures above. 



Depressor Caudae (Fig. 23, No. 6). Location. The infero-lateral 

 side of the tail. 



Origin. From the lower half of the posterior border of the is- 

 chium, and from the entire posterior border of the post-pubis beyond. 



Insertion. To the quill butts of the three or four outer main 

 tail feathers. 



Shape. Strong, conical. 



Relations. -Externally, with the depressor coccygis. 



Action. Singly, pulls the tail downward and outward; with its 

 fellow, pulls the tail downward. 



Depressor Coccygis. Location. The outermost of the infero- 

 lateral muscles of the tail. 



Origin. From the lower half of the posterior margin of the ischium 

 and the anterior three-fourths of the posterior margin of the post- 

 pubic element of the pelvis beyond it. 



Insertion. To the thickened rim of the inferior and expanded 

 portion of the pygostyle. 



Shape. Flat, triangular. 



Relations. Internally with the depressor caudae. 



Action. Singly, pulls the tail downward and to one side; with its 

 fellow, pulls the tail downward. 



Lateralis Caudae (Fig. 23, No. 5). Location. The lateral side of 

 the tail. 



Origin. From the tip of the transverse process of the first free 

 caudal vertebrae. 



Insertion. To the outer three quill butts of the main tail feathers. 



Shape. Four fasciculi forming a fleshy belly. 



Relations. Inferiorly, with the levator caudae and superiorly with 

 the depressor caudae. 



Action.- Singly, pulls the tail downward and outward; with its 

 fellow, pulls the tail downward. The outermost fasciculus con- 

 tracting, spreads the tail feathers. 



Lateralis Coccygis (Fig. 2-5, No. E, 2). Location. The infero- 

 lateral side of the caudal vertebrae. 



Origin. From the surface of the posterior end of the ilium and by 



