334 



ZOOLOGY 



SECT. 



f. 



FIG. 945. Diagram of heart of Turtle. 

 a, incomplete ventricular septum ; C. p. 

 ca-vum pulmonale ; C. r. cavum venosum; 

 L. A. left auricle ; L. ao. left aortic arch ; 

 P. A. pulmonary artery; R. A. right 

 auricle ; s, arrow showing the course .of 

 blood in left aorta ; t, in right aorta ; 

 v. v'. auriculo-ventricular valves ; w, 

 arrow showing the course of blood in left 

 auriculo-veutricular aperture ; x, in 

 right ; y, between cavuni venosum and 



r.cct,r 



i.ca.r 



the ventricle contracts, its walls come in contact with the edges of 

 the septum, and the cavum pulmonale becomes cut off from the 



rest of the ventricle. The further 

 contraction consequently results 

 in the venous blood of the cavum 

 pulmonale being driven out 

 through the pulmonary artery to 

 the lungs, while the blood that 

 remains in the remainder of the 

 ventricle (arterial and mixed) is 

 compelled to pass out through 

 the aorta. But in the Crocodilia 

 (Fig. 946) the cavity is completely 

 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 



arSry. "^ffiSS^S " ^^^ the ^ a rtlc **<& ^ The 



right and left arches cross one 



another and where their walls are in contact is an aperture- 

 the foramen Panizzce placing their cavities in communication. 



The brain of Rep- 

 tiles is somewhat 

 more highly organ- 

 ised than that of the 

 Amphibia. The brain 

 .substance exhibits a 

 distinction into su- 

 perficial grey layer 

 or cortex, containing 

 pyramidal nerve cells, 

 and central white 

 medulla, not observ- 

 able in lower groups. 

 The cerebral hemi- 

 spheres are well de- 

 veloped in all. The 

 mid-brain consists 

 usually of two closely- 

 approximated oval 

 optic lobes ; rarely it 

 is divided superfici- 

 ally into four. The 

 cerebellum is always of small size, except in the Crocodilia 

 (Fig. 947), in which it is comparatively highly developed, and 

 consists of a median and two lateral lobes. 





FIG. 946. Heart of Crocodile with the principal arteries 

 (diagrammatic). The arrows show the direction of the 

 arterial and venous currents. I. aort. left aortic arch ; 

 I. aur. left auricle ; /. aur. vent. ap. left auriculo-ventri- 

 cular aperture ; ?. car. left carotid ; I. svb. left subclavian ; 

 I. vent, left ventricle ; pul. art. pulmonary artery ; r. aort. 

 right aortic arch ; r. aur. right auricle ; r. aur. vent. up. 

 right auriculo-ventricular aperture ; r. car. right carotid ; 

 r.sub. right subclavian; r. vent, right ventricle. (From 

 Hertwig's Lehrbuch.) 



