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-arm. 



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 metacarjpi radialis longus, a 

 muscle forming the anterior or preaxial edge of the fore- 

 arm, and acting as extensor of the manus. 



