COMMON GANNET. 



63 



The sterno trachealis, Fig. G, A, s s, is well de\-eloped and there is a thin strip of a bronchialis arising at 

 the base of the lower side of the sterno trachealis and extending over the two upper laryngeal half rings, 

 see Fig. G, 15. Eelow these muscles, and adhering to the sides t f the larynx arc tv.o singular hemispherical 

 bodies, yellowish white in color, see Fig. G, A, c c, where a view of the lower side is given. 



These organs have been considered by some authors as the rudiments of a second pair of thyroid glands. 

 I am inclined, however, to thhik them the shrunken thymus glands only, as they contain an oily matter. es- 

 pecially as the thymus glands are enormously developed in the young gannets. The question can be easi- 

 ly settled by examining the young of the Common Gannet when a few days old, and later, in order to note 

 the gradual diminution of the thymus. It is quite possible that it may have an attachment to this portion 

 of the larynx from the first, but what function it can have thus attached is difficult to determine; at all 

 events, it appears to be unique in this gannet as no other species of bird, either in this genus or in any 

 other, which has come under my notice has anything like it. 



Fig, 8. 



Fig. .1. Fig. KK 





Fig. 11. 



This gland is not attached to the larj-nx by its entire base, but adheres only along its upper side, see 

 Fig. G, C, where I have given a view of the left side of the larynx with the gland removed: the shaded por- 

 tion at c, shows the points of adhesion. Beneath the gland, and partly covered by it, is a vibrating mem- 

 brane, lying between the third and fourth bones of the larjTix, see Fig. G, C, u, wliere there is an outside view 

 of the vibrating surface, and E, u, where is given an inside view, c, being the gland. On the lower side of 

 the glands, is an open orifice that extends over the membrane, back to the point of attachment of the gland 

 to tiie larj-nx. Fig. 6, A,rr. At B, c, is given a side view of the gland. 



The bronchial tubes are long, Fig. 7. A, b b, and are composed of about twenty-three half rings. They 

 diverge at the junction with the larrax, at a considerable angle: see Fig. 7, C, o, where is given a view of 

 the upper portion of the larynx, the other parts being lettered as in the other figures. Below, the division 

 is concealed by the lower bone of the larynx, Fig. G, A, t. At their junction with the larynx, the bronchial 

 tubes are narrow. Fig. 7,C, d. but rapidly become wider, Fig. 7, d, and Fig.G, A, b b. 



