THE PIGEON. 249 



they form the actual supports of the glottis. The two anterior rings 

 of the trachea are incomplete dorsally, and the first has its dorsal 

 extremities fused with the thyroid. 



XLIX. Cut away the outer wall of one of the nasal 

 cavities, first passing a probe from the anterior to 

 the posterior nares : note : 



304. The elevation caused by the turbinal (§ 72), covered 

 by the delicate Schneiderian membrane. 



305. The relations of the anterior and posterior nares 

 to the nasal cavity. 



L. Remove the dorsal wall of the orbit : observe 

 the four straight and two oblique muscles, which 

 have the same relations as in the lower vertebrata 

 (see pp. 77, 78, §§191 — 203): remove the eye with 

 the nictitating membrane by cutting through its 

 muscles and the optic nerve : observe : 



306. The lacrymal gland, a whitish irregular body in 

 the postero-dorsal region of the orbit. 



307. The Harderian gland, a small pinkish body in 

 the anterior region of the orbit. 



308. The form of the eye : its inner half has the usual 

 hemispherical figure, but its outer half is somewhat obtusely 

 conical. 



309. The entrance of the optic nerve, in the centre of 

 the inner hemisphere. 



310. The bursalis, a somewhat quadrate shoot of 

 muscle, arising from the dorsal region of the inner hemi- 

 sphere by a convex edge, and passing downwards to end in 

 a concave edge just over the optic nerve: the lower edge 

 forms a tubular tendinous sheath. 



311. The pyramidalis, a triangular muscle, arising 

 from the antero-ventral region of the inner hemisphere ; it 

 passes upvv-ards and baclcwards, and, just in front of the 



