DIGESTIVE SYSTEM. 441 



Note also, and preserve the posterior mesenteric vein, 

 which runs in the mesenterial fold connecting the rectum 

 with the dorsal wall of the abdomen. 



1. The oesophagus commences at the hinder part of the 



buccal cavity, and runs back through the neck and 

 thorax to the stomach. In the neck it is thin- 

 walled, and dilates behind to form a large bilobed 

 sac, the crop. In the thorax it has thick walls. 



2. The thyroid gland is a paired structure at the base of 



the neck. 



3. The stomach, or proventriculus, lies dorsal to the left 



lobe of the liver : it is rather wider than the oeso- 

 phagus, and has thick glandular walls, in which 

 the gastric juice is secreted. Attached to the right 

 side of the proventriculus is a small red body, the 

 spleen. 



4. The gizzard is a large hard body, somewhat flattened 



laterally, and with very thick muscular walls, the 

 muscular fibres radiating outwards from a bluish 

 tendon in the centre of each lateral surface. It 

 forms a powerful mill for grinding the food. 



The proventriculus opens into the gizzard at its 



Fig. 75. Columba livia. Dissection of the male from the right side. 

 Half the liver and the greater part of the intestine have been 

 removed. In the right wing the bones and the arrangement of the 

 primary and secondary feathers are shown. The reproductive 

 organs are omitted, (a. m. m.) 



A, nostril. AD, ad-.digital primary feather. B, external auditory meatus. 

 BW, bastard wing. C, oesophagus. CA, right carotid artery, d, crop. DA, 

 aorta. E, keel of the sternum. F, right auricle. G, right ventricle. HV, 

 hepatic vein. H 1, left bile-duct. H 2, right bile-duct. |, distal end of 

 proventriculus or stomach. |A, right innominate artery. |V, posterior vena 

 cava. JA, left innominate artery. Jv, right jugular vein. K, gizzard. |_, 

 liver. M, proximal limb of duodenum. MD the two mid-digital primary 

 feathers. MP, the six metacarpal primary feathers. M 1 , preaxial metacarpal. 

 M 2, middle metacarpal. M 3, postaxial metacarpal. N, cloacal aperture. 

 N 1 , preaxial digit of manus. O, bursa Fabricii. O 1 , proximal phalanx 

 of middle digit of manus. O 2, distal phalanx of middle digit of manus. P. 

 pancreas. PA, right pectoral artery. PD, pre-digital primary feather. PV 

 portal vein. P 1, first pancreatic duct, p 2, second pancreatic duct. P 3. 

 third pancreatic duct. Q, pygostyle. R, rectum. RC, radial carpal bone . 

 RX, rectrices or tail-feathers. R 1, ulnar digit of manus. S, ureter. SA, 

 right subclavian artery. SV, right anterior vena cava. T, rectal diverticulum. 

 U, kidney. UC, ulnar carpal bone. V, pelvis. W, lung. X, humerus. Y radius. 

 Z, ulna. 



