554 



ANURA 



[CH. 



Ml 



the left auricle has been driven 

 over to the opening of the conus 

 from the left side of the ven- 

 tricle, and so mixed blood passes 

 to the hinder portion of the 

 body. When the pressure in the 

 ventricle rises to its highest 

 point, the last blood, which is 

 almost completely arterial, all 

 from the right auricle having 

 been driven out, is able to 

 overcome the resistance in the 

 carotid gland and go to the 

 head, which contains the organs 

 having the greatest need for 

 thoroughly oxygenated blood. 



The posterior cardinal veins 

 are represented only by their 

 hinder portions, the renal por- 

 tals, all the blood from the 

 kidneys being carried to the 

 heart by the inferior vena cava. 



The brain of the Frog and 

 of Anura in general is more 

 highly developed than that of 

 the Urodela. Thus (Fig. 275) 

 the olfactory lobes of the cere- 

 bral hemispheres are connected 

 together, and the optio^lobes of 

 the mid-brain are well TO^eloped- 



It was pointed out (p. 



FIG. 275. Brain and spinal cord of a gene- 452) that the limbs of 

 ralised Anuran. In the Phaneroglossa the . ,. 



1st spinal nerve is suppressed, x about 2. Vertebrates are 111 all 



a. Cerebral hemisphere. b. Olfactory lobe, probability derived from 



, l a t pra l 

 two te] 



O f 



c. Eye. d. Thalamencephalon. e. Optic 

 lobes. f. Cerebellum. g. Medulla 



oblongata. h. Fourth ventricle, i. Spinal that is, two longitudinal 



cord. i. Olfactory nerves. n. Optic mu i xi, 



nerve, m. Oculomotor nerve, iv. Path- fins. I he muscles m these 



eticus. v. Fifth nerve. vn. Facial fins were originally pro- 



nerve. vin. Auditory nerve, ix. Glosso- -, , f ,-' 



pharyngeal nerve. x. Vagus nerve, longations of the myo- 



110. First to tenth spinal nerves. 2 and tomes, and the nerves were 



3 unite to form the brachial, and "7, 8, 9 

 and 10, to form the sciatic plexus. 



of course branches of the 



