454 ZOOLOGY stecf. 



ultimate branches of which, or terminal bronchioles, opens into 

 a minute chamber or infundibulum, consisting of a central 

 passage and a number of thin-walled air-vesicles or alveoli 

 given off from it. A group of these infundibula, supplied by a 

 single bronchiole, which divides within it to form the terminal 

 bronchioles, is termed a lobule of the lung. 



In shape the lung may be roughly described as conical, with the 

 apex directed forwards. The base, which is concave, lies, when 

 the lung is distended, in contact with the convex anterior surface 

 of the diaphragm. The outer or costal surface is convex in adapta- 

 tion to the form of the side-wall of the thorax ; the internal surface 

 is concave. 



Ductless Glands.- The spleen is an elongated, compressed, 

 dark-red body situated in the abdominal cavity in close contact 

 with the stomach, to which it is bound by a fold of the peritoneum. 

 The thymus, much larger in the young rabbit than in the adult, is 

 a soft mass, resembling fat in appearance, situated in the ventral 

 division of the mediastinal space below the base of the heart. The 

 thyroid is a small, brownish, bilobed, glandular body situated in 

 close contact with the ventral surface of the larynx. 



Nervous System. The neural cavity, as in the Pigeon, con- 

 tains the central organs of the cerebro-spinal nervous system 

 the brain and spinal cord. The brain (Figs. 1105-1107) of the 

 Rabbit contains the same principal parts as that of the Pigeon, 

 with certain differences, of which the following are the most im- 

 portant. 



The surface of the cerebral hemispheres or parencephala (Fig. 

 1105, /. 6., Fig. 1106, c.h.), which are relatively long and narrow, 

 presents certain depressions or sulci, which, though few and in- 

 distinct, yet mark out the surface into lobes or convolutions not 

 distinguishable in the case of the Pigeon or the Lizard. A slight 

 depression the Sylvian fissure at the side of the hemisphere 

 separates off a lateral portion, or temporal lobe (Fig. 1107 c. h 2 .), 

 from the rest. There are very large club-shaped olfactory bulbs at 

 the anterior extremities of the cerebral hemispheres, and behind 

 each on the ventral surface of the hemisphere is the corresponding 

 olfactory tract leading back to a slight rounded elevation, the 

 tuberculum olfactorium. Connecting together the two hemispheres 

 is a commissural structure the corpus callosum (Figs. 1106, 1107, 

 cp. cl.) not present in the Pigeon ; this runs transversely above 

 the level of the lateral ventricles. Examined in transverse section, 

 i.e., in a longitudinal section of the brain (Fig. 1107), the corpus 

 callosum is seen to bend slightly downwards, forming what is 

 termed the genu ; posteriorly it bends downwards and forwards, 

 forming the splenium, which passes forwards and is united with the 

 fornix. Below the corpus callosum is another characteristic struc- 

 ture of a commissural nature the fornix (b.fo.) a narrow median 



