232 A. G. POHLMAN 



Accordino; to Geoffry Smith ('04) : The cohimella is provided with a 

 single muscle. The M. tensor tj^mpani, which attaches to the infra- 

 stapedial and the drum margin between the infra- and extrastapedial 

 cartilages. The muscle passes out of the ear through a wide opening, 

 close to the foramen stylo-mastoideum, bends to the posterior surface 

 of the skull, and attaches to the basioccipitale in a gentle depression 

 which extends almost as far as the condylus occipitalis. 



I will confine the description of this questioned muscle for the 

 most part to its relations in the pigeon and chick which I have com- 

 pared with a few other forms. Inspection of the figures given by 

 Breschet shows that here, as well as in the relations of the organ of 

 hearing itself, a very great similarity exists in the various classes of birds. 



The sound-transmitting apparatus, which lies between the drum and 

 the labyrinth, is formed by the columella. This resembles a mam- 

 malian stapes provided with a long stalk and attached laterally to a 

 cartilaginous apparatus which has been homologized in part with the 

 malleus and incus. This cartilage may be called the cartilage-head 

 of the columella (extra-stapedial of Huxley). Its figure is that of an 

 obtuse angle triangle with one point and the baseline attached to the 

 drum. The latter is placed radially in the posterior-inferior quadrant 

 of the drum membrane which is thickened between the head of the 

 columella and the drum margin by tendinous fibres. Cartilaginous 

 processes arise from either side of this structure posteriorly and inferi- 

 orly, somewhat raised on the inner surface of the drum and attached 

 to the borders of this membrane. Just as the struts support the can- 

 vas of a tent, so the head of the columella together with its carti- 

 laginous processes press the drum outward, and indeed even after the 

 columellar stalk has been severed, the elasticity of the cartilage-head 

 and its processes is sufficient to maintain the drum convexity. 



If one divides the drum by two diagonal lines, four quadrants result 

 which are somewhat different in structure. The ventral upper quad- 

 rant forms a regularly stretched conical mantle; the lower is flaccid; 

 while the posterior quadrant is thickened by tendinous fibres partic- 

 ularly near its margin. The M. tensor tympani arises, as described by 

 Gadow, from the outer surface of the skull close to the condyle; is 

 directed horizontally forward and lateralward toward the bony border 

 attaching the drum membrane. The Nn. glossopharyngeus and vagus 

 emerge from the skull at its lower border. The muscle passes through 

 an opening in the bony border of the external auditory canal and sends 

 its tendinous fibres to attach to the drum margin medially below the 

 columellar head. It therefore never enters the tympa];iic cavity as 

 described by Breschet. The tendon breaks up in a sort of pes anserinus 

 which unites with the drum; the upper portion however coming from 

 below and behind unites to the manubrium-like process of the head of 

 the columella. 



The muscle is innervated by the N. facialis and may be stimulated 

 wdth ease and certainty through the trunk of this nerve. This may be 

 accomplished through a dissection exposing the semicircular canals and 



