=Rectus Superior= (Fig. 26, No. _B_, 1). (Synonym.—Rectus dorsalis.) _Location._—Superior to the eyeball. _Origin._—Along the supero-posterior border of the optic foramen. _Insertion._—To the sclera just within the margin of the bony circle of the eye. _Shape._—Flat, thin. _Relations._—Internally, with the obliquus superior; superiorly, with the bony wall of the orbit. _Action._—To pull the eyeball upward. =Rectus Inferior= (Fig. 26, No. _B_, 3). (Synonym.—Rectus ventralis.) _Location._—Inferior to the eyeball. _Origin._—From the inferior border of the optic foramen. _Insertion._—To the lower portion of the eyeball within the margin of the bony circle of the eye. _Shape._—Thin, fan-shaped. _Relations._—Superiorly, with the eyeball; inferiorly, with the bony wall of the orbit. _Action._—Pulls the eyeball downward. =Rectus Externus= (Fig. 26, No. _B_, 4). (Synonym.—Rectus lateralis.) _Location._—External to the eyeball. _Origin._—By two heads infero-laterally to the optic foramen. _Insertion._—To the postero-external 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 Internus= (Fig. 26, No. _B_, 2). (Synonym.—Rectus medialis.) _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 external ear. _Origin and Insertion._—The circumconcha, surrounding the periphery 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 tympanum. _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.