XXII l] LACERTA VIVIPARA 581 



partitions or septa. One is the continuation of the division between 

 the two auricles, the other is a ridge which arises from the ventral 

 side and tends to separate the opening of the pulmonary arteries 

 from that of the right and left aortic arches. When the ventricle 

 at first begins to contract it is full of venous blood from the right 

 auricle : by the time arterial blood has commenced to enter it from 

 the left auricle, the ventral septum mentioned above has been 

 driven against the opposite wall, so as to shut off the pulmonary 

 trunk from the rest of the ventricle and prevent its receiving any 

 more blood. The left aortic arch, which arises on the right, re- 

 ceives mostly venous blood from the right auricle, whilst the right 

 aortic arch arising on the left receives arterial blood from the left 

 auricle, and it is from this arch, as mentioned above, that the 

 carotid arteries arise. Hence the head receives comparatively 

 arterial blood, and all the rest of the body mixed blood. The 

 lingual artery of Amphibia is represented in Reptiles by a vessel 

 (tracheolingual or "ventral carotid") which arises from the carotid 

 arch near the middle line and supplies the tongue, trachea and 

 muscles of the neck and shoulder. 



The vessels supplying the fore-limb arise together from the 

 right systemic arch in the case of Lizards instead of as in Anura 

 from both right and left arches ; they are subclaviaus of the dorsal 

 type (see p. 431), but in Chelonians and -Crocodiles the subclavians 

 are ventral in origin, coming off from the carotid trunk on either 

 side close to its division into ventral and dorsal carotids. In 

 Lizards this "ventral subclavian" is represented by the scapular 

 artery which runs to the shoulder region. 



The veins, on the whole, closely resemble those of Molge, 

 There is however no large cutaneous vein, and the external jugular 

 veins are represented by a median inferior jugular vein which opens 

 into the right anterior vena cava. The anterior part of the posterior 

 cardinal, now called the vena azygos, is found only on the right 

 side, where it receives the numerous intercostal veins, returning the 

 blood from the muscles connecting the ribs. The renal portal, 

 sciatic, femoral and anterior abdominal veins have the same 

 arrangement as in the Urodela. 



The brain is distinguished by the comparatively large size of the 

 cerebral hemispheres, which overlap the thalamencephalon above and 

 at the sides. They end in front in large pear-shaped olfactory lobes. 

 The cerebellum is a high vertical ridge and is thus much more 

 prominent than in any Amphibian. The remainder of the hind-brain, 



