THE PIGEON. 251 



tympanic cavity is reached, a small chamber, separated 

 from the external meatus by the tympanic membrane, and 

 communicating with the cavity of the mouth by the Eus- 

 tachian tube ( 298), into which a bristle should be passed. 



319. The relations of the columella to the tympanic 

 cavity (see 61, p. 195). 



LIII. Carefully remove the skin from the shoulder and 

 wing, and dissect oft' the fascia, a strong sheath 

 of connective tissue which covers the muscles, 

 until the following can be made out : 



320. The tensor patagii longus, a small conical slip 

 of muscle, arising from the antero-external region of the 

 pectoralis major : it receives fibres from the tensor patagii 

 brevis ( 325), and passes distally into a long elastic tendon, 

 lying in the border of the alar membrane ( 135), and in- 

 serted into the skin on the pre-axial border of the manus. 



321. The biceps, a large muscle forming the fleshy 

 mass in the anterior border of the upper arm, and acting as 

 the chief flexor of the fore-arrn. 



322. The triceps, forming the fleshy mass on the poste- 

 rior aspect of the upper arm, and acting as extensor of the 

 fore -arm. 



323. The tensor patagii accessorius, a small 

 squarish mass of muscle lying in the proximal region of the 

 alar membrane : it arises from the fascia of the biceps ; its 

 anterior border is connected by fascia with the tendon of 

 the tensor longus, and from its posterior border a long stout 

 tendon is given off which passes outwards, soon becoming 

 parallel to the tendon of the tensor longus, and having a 

 common insertion with it. 



324. The extensor metacarpi radialis longus, a 

 muscle forming the anterior or preaxial edge of the fore- 

 arm, and acting as extensor of the manus. 



