176 Description of the Plates. 



a perfect diaphragm, and also of a corpus callosum, — Birds and 

 Reptiles resemble each other as closely as they do in the micro- 

 scopic character of their blood-corpuscles. In two points of second- 

 ary importance Birds resemble the Loricate and differ from the 

 Squamate Reptiles ; in this latter class there is a rudimentary 

 urogenital apparatus, and the genital gland is situated a certain 

 distance anteriorly to the kidney ; whilst in Birds, Crocodiles, and 

 Chelonia, the genital and urinary glands have separate outlets, 

 and the glands themselves are more or less completely in appo- 

 sition with each other. On the other hand, all Birds possess a 

 quadrilocular heart, and a single aorta belonging to the left ven- 

 tricle, an arrangement by which they are secured against any 

 direct admixture of venous with arterial blood, and in which they 

 differ as widely and constantly from Reptiles as in the peculiarity 

 of their integumentary system. 



No Reptiles possess a true crop, such as is seen at b in the figure, 

 nor two coeca ; but these structural arrangements are by no means 

 constant in Birds. 



a. Right cerebral hemisphere. Its surface is smooth, contrasting 



herein with that of the transversely laminated cerebellum 

 seen behind in the median line. 



b. The crop, which is bilocular in the Colimibidae. It is con- 



tinuous above with an artificially distended oesophagus, and 

 a window has been made in its right wall to show its divi- 

 sion into two compartments. 



c. Right lobe of liver, on which the right side of the heart 



rests. 



d. Heart. The ventricular portion is more acutely conical in 



most Birds than in Mammals, and the auricles are smaller 

 in relation to it. 



e. Loop of duodenum in which are contained the longitudinally 



arranged lobes of the pancreas. Into this loop of intestine 

 three ducts open from the pancreas and two from the liver, 

 which has no gall-bladder in this species. Two of the pan- 

 creatic ducts open near the middle of the distal segment of 

 the duodenum close to each other and to one of the gaU- 

 ducts; the third pancreatic duct opens near the distal end 

 of the loop, and the second gall-duct near its proximal end. 



