128 ANATOMY OF THE DOMESTIC FOWL 



Origin. — By two heads infero-laterally to the optic foramen. 



Insertion. — To the postero-extemal side of the eyeball. 



Shape. — Short, fan-shaped. 



Relations. — Internally, with the eyeball; externally, with the bony 

 wall of the orbit. 



Action. — Pulls the eyeball outward. 



Rectus Intemus (Fig. 26, No. B, 2). (Synonym. — Rectus 

 mediahs.) 



Location. — Inner side of the eyeball. 



Origin. — From the supero-anterior border of the optic foramen. 



Insertion. — To the sclera on the anterior portion of the eyeball. 



Shape. — Thin, fan-shaped. 



Relations. — Internally, with the eyeball and with the pyramidalis; 

 externally, with the bony wall of the orbit. 



Action. — ^Pulls the eyeball inward. 



THE MUSCLES OF THE EAR 

 Circumconcha Tensor tympani 



Circumconcha (Fig. 7, No. 32). Location. — Surrounds the exter- 

 nal ear. 



Origin and Insertion. — The circumconcha, surrounding the periph- 

 ery of the ear, is adherent to the skull and loosely to the skin, and 

 is attached to the outer terminus of the supra-occipital crest. 



Relations. — Internally, with the skull; externally, with the skin. 



Action. — Relaxes the tympanum. 



Tensor Tympani (Fig. 7, No. 31). Location. — ^External to the 

 quadrate and to the external auditory meatus. 



Origin and Insertion. — From the surface of the quadrate and the 

 inner end of the quadrato-jugal to the inner surface of the tjonpanum. 



Shape. — ^A few fibers. 



Relations. — ^Internally, with the quadrate and the quadrato-jugal; 

 externally, the integumental duplicature. 



Action. — ^Tenses the tympanum. 



FUNCTIONS OF MUSCLES 



To cause the feathers on the top of the head to lie flat: 



Dermo-frontalis. 

 To raise the feathers along the superior part of the neck and along the dorsal 

 region: 



Dermo-dorsalis. 



