Description of the Modifications of certain Organs. 641 



outside the larynx. A median sac is formed by a second dilatation 

 of the left large sac, and is partly covered by the somewhat hoUowed 

 out basibyal bono. In other Catarrhinae an uni)aired pouch is in 

 direct cominunication with the hirynx through an aperture at the 

 base of the epiglottis, and is received by a corresponding cavity of the 

 basihyal, which howcver never assumes anythiug like such an excessive 

 Inflation as in Mycetes. Not all these laryngeal sacs are therefore 

 strictly homologuous formations, and they seem to have been develop- 

 ed independently by various groups of Monkeys. 



6. The stomach of the Ostrich. 



The peculiar and almost unique shape and position of the stomach 

 of the African Ostrich has been described by various anatomists, not- 

 ably by Meckel^), Macalister^)^ and myself^). 



While in the typical position of the avine stomach the gizzard follows 

 lower down upon the proventriculus, and is frequeutly separated from 

 it by a glandless space or „Zwischenschlund" of oesophagcal structure, 

 the proventriculus of the Ostrich is enormously dilated and situated 

 dorsally from the gizzard. The glandulär area, not rarely, e. g. in Rhea, 

 restricted to a circuniscript region in the dorsal wall of the Oesophagus, 

 is somewhat dumb-bell shaped, and contains about 300 orifices of 

 Compound glands, which, instead of being placed closely together, are 

 rather separated from each other, and occupy only about the dorsal 

 quarter of the proventricular wall. The portion, which corresponds 

 with the „Zwischenschlund" of other birds, is drawn out into a thin- 

 walled bag, the blind eud of which reaches considerably to the tail- 

 ward from the gizzard. The openiug into the gizzard looks tailwards 

 instead of towards the heart. The gizzard itself is small but extre- 

 mely muscular; one tendinous speculum, that of the pyloric or right 

 side, looks towards the heart and right side, but is situated above 

 the pylorus instead of below it; the morphologically left speculum 

 looks ventrally, and likewise somewhat towards the right side. The 

 strong furrow, which in all birds with a strongly muscular gizzard 

 niarks the line of junction of its two lateral muscles, and partly pro- 

 jects into the lunien of the gizzard, looks obliquely headwards instead 



1) J. F. Meckel, System der vergleichenden Anatomie, 1829. 



2) A. Macalister, in: Proceed. Roy. Irish Acad., vol. 9, 1869. 



3) H. Gadow, in: Jenaische Zeitschrift f. Naturwiss., Bd. 13, 1879; 

 and Bkonn's Klassen und Ordnungen des Thierreichs, Vögel. 



