360 



ZOOLOGY 



SECT. 



aorta. But in the Crocodilia (Fig. 3 003) tlie cavity is com- 

 pletely divided, so that there we may speak of distinct right 

 and left ventricles. From the right arises the pulmonary artery 

 and the left aortic arch : from the left the right aortic arch 



only. The right and left arclies 

 cross one other, and where their 

 walls are in contact is an 

 aperture — the foramen Panizzce 

 — placing Iheir cavities in com- 

 munication. 



The brain of Reptiles is some- 

 what more highly organised than 

 that of the Amphibia. The brain 

 substance exhibits, a distinction 

 into superficial grey layer or cor- 

 tex containing pyramidal nei've- 

 cells, and central white medulla, 

 not observable in lower groups. 

 The cerebral hemispheres arc 

 well developed in all, and there is 

 a hippocampus (see helow in the 

 description of the brain of the 

 Rabbit, and of that of the Mam- 

 mals in general) in the shape of 

 a specially modified region of the 

 dorsal and mesial walls of each 

 hemisphere, represented less dis- 

 tinctly in the Amphibia ; a com- 

 missure — the hippocampal — con- 

 nects the hippocampi of opposite 

 sides, and is dorsal to the chief 

 cerebral commissure — the an- 

 terior covimissure. The mid-brain 

 consists usually of two closely- 

 approximated oval optic lobes ; 

 rarely it is divided superficially 

 into four. The cerebellum is 

 always of small size, except in 

 the 'Crocodilia (Fig. 1004), in 

 which it is comparatively highly 

 developed, and consists of a 

 median and two lateral lobes. 

 Sensory Organs. — In most Lacertiiia, but not in the Ophidia, 

 the nasal cavity consists of two parts — an outer or vestibule, and 

 an inner or olfactory chamber — the latter having the sense-cells in 

 its walls, and containing a turbinal bone. In the Turtles each 

 nasal chamber is divided into two passages, an upper and a lower, 



FiQ. 1004.— Biain of AUigator, fiom 

 above. 11, ol. olfactory bulb; G.2\ epi- 

 physis ; ////, cerebellum ; MeO., spinal 

 cord : Mil, optic lobes ; Nil, medulla 

 oblongata ; VH, cerebral hemispheres ; 

 / — X /, cerebral nerves ; 1,2, first and 

 aecorid spinal nerves. (From AVieder- 

 shcim's ComjianUii-i^ Anatomy.) 



