It is lengthened out and unilobed in the Ophidia and the Amphisbaenoidea. There is always a gall-bladder which lies removed at some distance from the liver in the two groups just named. The pancreas has several ducts in some Chelonia and the Crocodilia.

1 Trionyx (Chelonian) is stated by Wiedersheim to have embryonic teeth.

The larynx consists of two arytenoid cartilages borne upon a cricoid ring composed of several united tracheal rings. The trachea is long, and in some Crocodiles and Chelonia forms a bend or loop. It and the two bronchi into which it divides are supported by cartilaginous rings, sometimes imperfect, and often united to one another by processes. The lungs are 'either simply saccular with ridges (primary, secondary, etc.) on the walls, upon which the capillaries are distributed, as in Ophidia and most Lacertilia: or the bronchus enters the inner side of the lung, traverses it, retaining cartilaginous semi-rings for a greater or less distance, and giving off eparterial and hyparterial bronchia which divide further as in some of the larger lizards, e. g. Regenia, and in Chelonia and Crocodilia. In some of the serpentiform lizards, e.g. Anguis, the left lung is shorter than the right This is the case also in the larger Ophidia, but in the majority of that order the left lung is a mere rudiment; and the posterior part of the right lung is thin and membranous and supplied by blood from the dorsal aorta.

In the Chamaeleons and some Geckoes delicate saccular prolongations arise from the inner side and posterior extremity of the lungs and lie among the viscera, foreshadowing the air-sacs of birds. Indeed in the Deinosaurian family Coeluridae the bones- of the skeleton are pneumatic to a greater degree than in the majority of birds. The lungs of the Chelonia lie at the back of the thorax and are invested by peritoneum on their ventral surface only. Strong muscular fibres spread into this investment and originate from the ribs. The Crocodilia possess pleural sacs.

There is a sinus venosus in the heart which opens by a bivalved aperture into the right auricle and receives the vena cava inferior and the two cava superiores, except in the Ophidia where the left cava superior opens separately into the auricle. The septum between the auricles is complete, and the left receives only arterial blood from the lungs. There is a complete ventricular septum in the Crocodilia, and the pulmonary artery and left aorta arise from the right or venous ventricle, while the right aorta is derived from the left or arterial ventricle. The two aortae communicate, however, at their roots by the foramen Panizzae. In other Reptilia there is no complete ventricular septum, but a strong muscular ridge projects from the ventral wall of the ventricle, and is attached anteriorly between the roots of the pulmonary artery and left aorta. When the heart contracts this ridge or septum pulmonale cuts off a cavum pulmonale which contains purely venous blood from the rest of the ventricle which contains mixed blood or on its left side arterial blood.

The pulmonary artery rising from the cavum pulmonale is thus filled entirely by venous blood, whilst the roots of the two aortae are so disposed that the left aorta rising rather on the right contains more venous than arterial blood, and the right aorta, vice versa, more arterial. The apex of the ventricle is attached by a fibrous band to the pericardium. The whole heart is broad and flattened dorso-ventrally in Chelonia. The roots of the two aortae and pulmonary artery are closely united in Lacertilia, Chelonia and Crocodilia. In many Lacertilia, e. g. Lacerta, the third or carotid aortic arch is complete and falls into the fourth or aortic arch: in other Lacertilia and Reptilia there is no connection between the two. The right aortic arch gives off the carotids, except in the Lacertilia first mentioned, and the subclavian arteries which are absent in Ophidia, and then unites with the left aorta to form the subvertebral aorta. The left aorta gives off the caeliac artery before it unites with the right, and in Chelonia and Crocodilia the artery in question is of so large a size that it appears to be the continuation of the arch.

In the Crocodilia the left aorta arising from the right ventricle carries only venous blood to the viscera, whilst in other Reptilia it carries a mixture of arterial and venous. There are always two venae cavae superiores. The cava inferior is formed by the union of the two efferent renal veins. There is a renal-portal circulation except in Chelonia. The caudal vein divides into two branches, each of which goes to the kidney of its own side in Ophidia; so too in the Lacertilia, but here each branch receives on the way the veins of the corresponding hinder extremity. In the Crocodilia the afferent kidney veins are derived from a transverse vessel uniting the two branches of the caudal. These are continued on into the two epigastric veins, remnants of the foetal umbilical veins, which receive the veins of the hinder extremity and conduct the blood to the liver, anasto-mising with the hepatic portal system. The two branches of the caudal vein are connected to the epigastrics in Chelonia. There is a single epigastric in Lacertilia which receives blood from the abdominal walls and the bladder and is distributed to the liver. The correspoding vein in Ophidia is resolved into a plexus, ramifying in the fat body (see p. 69) and receiving veins also from the abdominal walls.

Anastomoses exist, however, between the renal-portal veins and the rootlets of the hepatic portal system. The lymphatic vessels take the shape of loose sheaths or plexuses surrounding the large arteries, and communicate, as in Amphibia, with the superior cavae anteriorly and the ischiadic veins posteriorly. At their junction with the latter veins, contractile 'lymph-hearts' are developed. The Crocodile alone has a lymph gland which is situated in the mesentery. There are no valves to the lymph-vessels.