Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/476

Rh 458 REPTILES , [ANATOMY. margin of the jaws ami the palatines soon wear down to form mere enamelled cutting edges to the bones, with which they become immediately anchylosed. The extinct Dicynodonts, with their large iliaus FIG. 26. Skull of Chlamydosawus kingii (old male, from nature), showing jnucli differentiated teeth. 1, ventral aspect; 2, posterior; 3, profile, showing the enormous process at the hinder end of Hie lower jaw. canine-like teeth, growing from permanent pulps, behind the edentulous beak-like front part of the mouth, and those Ornitho- sauria which similarly have an edentulous beak in front of the toothed parts of their jaws, may but have carried out further and more completely that process of tooth reduction which we find to be effected with age in Hatteria. The liver consists of two lateral lobes. There is a pair of anal glands. a Croco- The Crocodilia have teeth in the max- illae, premaxillre, and mandible, but none in the palatines or pterygoids. They are implanted in distinct alveoli. The tongue is so flat and closely attached to the floor of the mouth that it can hardly be con- Fin l 7 -- Tw sidered as having a distinct existence. A to ' h f fle ' derma transverse fold of membrane extends along its hinder border and another similar fold descends in front of the posterior nares. There are no salivary glands. The oesophagus is wide, and the stomach nearly circular and gizzard-like, having thick muscular walls formed of fibres radiating from central tendons. The small intestine con- sists of two parts, an anterior part much convoluted, thin-walled, and lined with villi, which is succeeded by a thicker-walled part with internal zig-zag folds. There is no caecum, but a circular pro- minence marks the commencement of the large intestine, which is short and wide with a smooth lining. It is funnel-shaped, and opens by a very narrow aperture into a very elongated cloaca, the external opening of which is rather longitudinal. The liver, like that of Hatteria, is in two lobes, and the gall- bladder is beside the right lobe. The spleen lies behind the ridum (after Bocourt). 1, antcro-internal aspect of the tooth, showing a very deep longitudinal groove ; 2, pos- tero-extemal aspect of the masc tooth, showing a very faint longitudinal groove. pancreas between the folds of the duodenum. The various vi of the abdominal cavity lie, as in Birds, in separate serous sacs. 1 In the Chclonia there are horny sheaths to the jaws but no teeth, in C1n though numerous rudiments of teeth have been found in the Ionian embryo of Trionyx* The tongue is not extensible, but is differ- ently conditioned in different genera. There appears to be only a sublingual salivary gland, though the palate of the Land T<>! exhibits the apertures of numerous cutaneous follicles. The oesophagus leads to the left part of the transversely placed stomach. The extent of both the small and the large intestine varies; the latter is at its shortest in Trionyx. The cloaca opens externally by a somewhat rounded aperture. The liver is mostly large, and in two lobes connected by one or more transverse bands of its substance. The gall-bladder lies on its right and may be sunk within its substance. The pancreas has often several excretory ducts, and the spleen is generally of large size. The Respiratory System. All the Keptilia breathe air from the first moment of Rrspj their separate existence, and are never furnished withtorj anything in the shape of gills. The apparatus by which s y stet their respiration is effected is always a pair pf sacs or lungs Avhereof one sometimes aborts into dnd from which air is introduced and removed by the intervention of an azygous tube, the trachea, which, passing forwards ventrally to the oesophagus, or beside it, opens in the floor of the mouth behind the tongue. The more or less dilated most anterior portion of the azygous tube is the larynx, which may become a vocal organ. In the Lacertilia the external opening of the larynx mny, by in La rare exception, as in Phrynosoma, be placed in front of the hind- tilian most margin of the tongue, so that the larynx seems to per- forate that organ, but is in fact merely enclosed by the posterior, exterior, and median junction of two lingual processes. A mem- branous or cartilaginous epiglottis may protect the entrance to the larynx as in Mammals. The larynx may be composed of one cartilage, which is produced anteriorly into two arytenoid processes, but generally these latter are distinct cartilages. Folds of membrane or vocal cords may exist, as in the Geckos and Chameleons, and the latter have also a wide membranous sac connected with the larynx. The trachea is generally short, but may be long, as in Amphislsena and Lepidostcrnon. It is never convoluted, and its cartilages may or may not form complete rings. It ends posteriorly by dividing into two bronchi, which are usually very short, but maj r be of moderate length, as in Psammosaurus. The lungs are generally of about equal size, but in the Snake-like Lizards the right lung is the longer, and sometimes, as in Tyjildine and Acontias, the left lung may be quite rudimentary. The lungs may be simple bags or may give out lateral processes or pouches of varying extent. In the Chameleons their hinder halves arc prolonged into narrow tubular processes. Each lung is enclosed in a fold of peritoneum. The Ophidla have the opening of the larynx behind the tongue in rather prominent, with only a rudimentary epiglottis. The nature dian of their prey and their mode of eating do not readily expose them to the danger of small particles of food finding their way into the trachea. The cartilaginous framework of the larynx is very elongated. The trachea has its more anterior cartilages in the form of complete rings. The lungs are unsymmetrical in all the genera, but much more so in some than in others one lung entirely abort- ing in Typhlops, Acrochordus, and Vipcra amongst others. The two lungs are both of tolerable size in Python, Boa, and Eryx, which have the bronchi leading from the trachea to the two pulmonary sacs. These sacs may or may not be divided info subordinate cells towards the hinder end of each. Sometimes part of the trachea itself may be dilated dorsally into cellular promin- ences like an accessory lung, as in Hydroiiliis, or ventrally, as in Acrocliordus. A pulmonary sac may extend not only far back- wards but also forwards to the hyoidean region, as in Hcterodon. In the Chclonia the opening of the larynx or glottis is longi- in C tudinal. It may be furnished with a membranous epiglottis, orlmi may have none, as in Tcstudo. There may be cricoid and arytenoid cartilages in addition to main cartilages, but the details of structure differ in different genera. There arc no vocal cords. The trachea and bronchi vary in length, the former being long in most forms, the latter in Tcstudo. In Cinixys the trachea and bronchi arc contorted. The lungs are invested anteriorly and on their ventral side by peritoneum, and also by the diaphragm as they lie between it and the carapace, and therefore they do not project freely into the abdominal cavity. 1 Stannius pointed out emphatically, as long ago as 1856, tlie resem- blance which exists in many points between Crocodiles and Birds. See his Amphibien, p. 193, note 1. 2 See Owen, Odontoy., p. 179.