MIDDLE-EAR REGION OF GALLUS 231 



Brcschet) is not an intrinsic muscle of the tympanum, but arises 

 from and is applied to the outer surface of the skull. 



Breschet ('36) describes the muscle in the following manner: The 

 malleus (by which Breschet means the cartilaginous portion of the 

 columella attached to the drum) has strictly speaking a single muscle, 

 M. externus (laxator) memb. tympani. This muscle attaches to the 

 malleus at the union of the body of the l3one with the stalk of the 

 columella. Its tendon, at first fused to the drum, loses its connection 

 at the drum margin; passes into a bony canal; emerges from the tym- 

 panum; becomes fleshy; and attaches to the lower border of this cavity. 

 It is here covered by the Nn. glossopharyngeus and vagus. (There is 

 undoubtedly some error in the translation of the French into German. 

 The text itself was not available.) 



The inner muscle of the malleus (M. tensor tympani) is present only 

 as a rudiment. It is a delicate strand of connective tissue, particularly 

 prominent in the turkey where it is well separated from the drum mem- 

 brane. I have investigated it in other forms and have found it con- 

 stant and united with the drum as a glistening pearly streak. This 

 attaches to the malleus and runs forward and medialward; follows the 

 general direction of the Eustachian tube and merges with the fibro- 

 cartilaginous lining of the tube itself. The action of the muscle is 

 naturally a very limited one because it can propagate to the drum 

 only those movements imparted to it by the motion of the tubal walls 

 to which stout muscles are attached. It is hardly necessary to state 

 that, if one pulls upon this strand or upon the tubal walls to which it is 

 attached, the drum membrane becomes more tense. Traction upon 

 the tendon of the M. externus causes a relaxation of the drum; an 

 experiment which demonstrates the respective function of each. 



Gadow ('93) describes the muscle in the following manner: The 

 muscle is relatively stout; arises by fleshy fibres from the lower surface 

 of the OS occipitalis basilaris; and passes through a large opening into 

 the cavum tympani. The muscle renders the drum more tense and 

 draws it outward. The muscle corresponds to the M. tensor tympani 

 of the mammals, and is innervated by a fine twig of the ramus III of 

 the N. trigeminus. A M. stapedius, innervated by the N. facialis, is 

 wanting in birds. 



Gaupp ('98) remarks: It is difficult to believe that this description 

 is correct. It is in direct opposition to what is known of the middle 

 ear muscle of the Sauropsidans and above all is contrary to Killian's 

 positive statements. Furthermore, the innervation of a muscle 

 attached to the posterior border of the drum through the N. trigeminus 

 would be a remarkable thing. The notations of Killian, ('90) who 

 undoubtedly worked on this same muscle, give its nerve supply through 

 a separate branch of the N. facialis. Killian found this to be true in 

 duck, goose, and chicken, and describes the embryonic attachments of 

 the muscle first to the extrastapedial and later into the margin of the 

 drum membrane proper. 



JOURNAL OF MORPHOLOGY, VOL. 35, NO. 1 



