NERVOUS SYSTEM OF VERTEBRATES. 391 



called the lacteal system or absorbents, which take up a part 

 of the chyle from the digestive organs and convey it to the 

 blood-vessels. 



There is a true heart, with one, generally two, auricles, and 

 one or two ventricles with thick, muscular walls, and besides 

 arteries and veins, a capillary system, i. e., minute vessels 

 connecting the ends of the smaller arteries with the smaller 

 veins. There are no genuine capillaries in the lower animals 

 exactly comparable with those of the Vertebrates. 



The blood is red in all the Vertebrates except the lancelet, 

 and contains two sorts of corpuscles, the white corpuscles 

 like the blood-corpuscles of invertebrates, and red corpuscles 

 not found in invertebrates, and which are said by some 

 authors to be derived from the white corpuscles. 



While fishes and larval Amphibians breathe by gills, all land 

 and amphibious Vertebrates breathe the air directly by means 

 of cellular sacs called lungs, and connected by a trachea with 

 the pharynx, the trachea being situated beneath the oesopha- 

 gus, and the opening from the mouth into the pharynx lead- 

 ing into the trachea being placed below the throat or passage 

 to the oesophagus. The air filling the cells or cavities of the 

 lungs passes by osmose through the walls of the cells into the 

 blood sent by the heart through the pulmonary artery, and 

 after being oxygenated it returns by the pulmonary vein to 

 the heart. On the other hand, carbonic acid passes from 

 the blood out of the lungs through the trachea. 



The nervous system of Vertebrates consists of a brain and 

 spinal cord. The brain consists of four pairs of lobes, i. e., 

 the olfactory lobes, cerebral hemispheres, the optic thalami 

 (Thalamencephalon) and pineal gland, and the optic lobes; and 

 two single divisions : the cerebellum and the beginning of the 

 spinal cord, called the medulla oblongata. The olfactory lobes 

 are the most anterior, and send off the nerves of smell to the 

 nose. The cerebral hemispheres in the fishes and amphibians 

 are little larger than the adjoining lobes, but in the reptiles 

 become larger, until in the mammals, and especially in the 

 apes and man, they fill the greater part of the brain-box and 

 overlap the cerebellum ; the latter, in the mammals, also 

 exceeding all the other lobes in size, excepting the cerebrum. 



