02 COMPARATIVE ANATOMY. 



and differ from the corresponding parts of the Reptilian brain in 

 being in contact with the cerebellum, and also by reason of 

 their much greater size. The cerebellum is large, and divided 

 by numerouj transverse ' sulci ' into well-marked lobules. It 

 has no lateral lobes. The ' corpora bigemina,' instead of being 

 in contact with each other mesially, as is always the case in 

 other Vertebrates, are thrown down towards the infero-lateral 

 surface of the brain, so that they appear as rounded lateral 

 projections. The other points to be noted about the head, 

 which is supported upon a long neck consisting of more than 

 seven vertebrae, are the presence of feathers ; the absence of 

 a ' concha ' to the external auditory meatus ; a well-developed 

 third eyelid, which can be drawn vertically across the eye ; 

 the edentulous character of the mouth ; the horny and non- 

 prehensile tongue ; and the absence of an epiglottis. The 

 widely dilated oesophagus expanding below into a bi-sacculated 

 crop occupies the front of the flexible neck. The cartilagi- 

 nous tracheal rings are complete. Between the chest and the 

 abdomen the absence of a diaphragm is to be remarked. In 

 the chest, and occupying a mesial position, is the long, acutely 

 conical heart. The short, thick aorta which it gives off, is seen 

 to divide into three large trunks, two 'arteriae innominate?,' 

 and a descending aorta. The aorta curves over the right 

 bronchus and not over the left, as in the Rat. Behind the crop, 

 and lying in close apposition with each other, in a deep groove 

 formed on the anterior surfaces of the cervical vertebrae by the 

 inferior transverse processes, are the two carotids. A piece of 

 blue paper has been placed beneath them. The right lung is 

 also seen in section. It is not divided into lobules, nor is it 

 suspended in a pleural cavity ; but is so firmly connected by 

 connective tissue to the back and side- walls of the chest as to be 

 marked by deep grooves, the impressions of the ribs. Each 

 innominate artery divides into three branches the carotid, sub- 

 clavian, and pectoral arteries. Below the heart is the liver, 

 composed, as in most reptiles, of a large right lobe and a smaller 

 left one, the two being connected by a transverse lobe. The 

 apex of the heart is received into a mesial depression between 

 the two lobes. Overlapped by the left lobe, and partially con- 

 cealed by it, is the thick-walled and muscular gizzard ; the 



