There is said to be an indication of a sixth digit in Chelonia and Lacertilia.
The cerebral hemispheres are smaller relatively to the rest of the brain, and to the spinal cord than in Aves, and the Deinosaurian Stegosaurus appears to have had a brain far smaller than the lumbar swelling in its own spinal cord, and smallest relatively to the bulk of the body among terrestrial Vertebrata. The olfactory lobes are well developed: the cerebral hemispheres are largest in the Crocodilia and some Lacertilia, and have a conspicuous corpus striatum. They are connected by an anterior commissure, and in the Crocodile there appears to be an indication of a fornix. The thalami optici are usually hidden by the cerebral hemispheres and optic lobes: the pineal gland is composed of non-nervous tissue and often attached to the dura mater. The optic lobes are hollow and the optic tracts often meet behind them dorsally. The cerebellum is either a mere transverse lamella, or of fair size and folded on itself. There is generally a bend between the medulla oblongata and the spinal cord. The ventricles of the brain are large. The spinal accessory nerve is not differentiated in Ophidia, and in most Reptilia the cervical sympathetic is double on both sides.
The nostrils lie usually at the apex of the snout, but just in front of the orbits in Plesiosauria and Ichthyosauria, or near them in Lguanodon. Many Lacertilia and the Ophidia have a nasal gland. The eyes are very small in some Ophidia (Typhlopidae, Uropeltidae) and Typhline among Lacertilia. In the Ophidia, the Geckoes, the Amphisbaenoidea, and some of the Scin-coidea among Lacertilia, the eyelids are transparent and united together forming a lacrymal chamber in front of the cornea. Other Scincoidea have the lower lid partially transparent. The third lid is present in many Lacertilia, in all Chelonia and the Crocodilia: and in the first-named is moved by a bursalis muscle attached to the orbit; but in the two other orders by a pyramidalis springing from the back of the eyeball itself. The Ophidia possess only the Harderian lacrymal gland. The sclerotic contains a ring of bones in the Ichthyosauria, Chelonia and in many Lacertilia. There is a pecten homologous with the similar structure seen in Aves in many Lacertilia: traces of it are said to be found in many Ophidia and the Crocodilia, but it is absent in Hatteria among Lacertilia and in Chelonia, an order in which the circular portion of the ciliary muscle only is developed.
A tympanic cavity is present except in Ophidia, Amphisbaenoidea and Hatteria. There are three Eustachian tubes in the Crocodile. The stapes is a rod-like bone, and when there is no tympanic cavity lies among the muscles. The tympanic membrane is exposed except in some Chelonia, the Ophidia, Hatteria and Chamaeleons, and is covered by a moveable flap in Crocodilia. The cochlea has the commencement of a spiral turn in Hatteria.
The Chelonia, the Cretaceous genus Pteranodon among Pterodactyls, and Oudenodon among the Dicynodontia, are edentulous1. The fore-part of both jaws is devoid of teeth in some Deinosauria, e. g. Iguanodon, and in some species of Rhamphorhynchus among Pterodactyls. A thickened epidermic sheath probably covered these parts as in the living Chelonia. Teeth are generally confined to the praemaxilla, maxilla and dentary, but in the Ophidia and some Lacertilia the palatine and pterygoid are den-tigerous also. They are anchylosed either to the edge of the jaw, e. g. Ophidia, many Lacertilia, or by their sides to a groove, e. g. Iguana; or are lodged in alveoli, e. g. Crocodilia, many Deinosauria; or in a shallow groove scarcely divided into alveoli as in Ichthyosauria. These forms of dentition are known respectively as acrodont, pleurodont, and thecodont. They are ranged usually in a single row, but there are exceptions as in some Ophidia. Anchylosis takes place by true bone, and, in Hatteria, when the teeth are worn away, the dense bone at the edge of the jaws forms an efficient substitute.
The enamel is often ridged and sometimes plicated at the base of the tooth in Lacertilia. Succession is vertical in Crocodilia, many Deinosauria; or the new tooth may take a lateral position as in the poison fangs of Ophidians. The two tusks of the extinct Dicynodon grew from permanent pulps, whilst the rest of the jaw was probably covered by thickened epidermis. The form of.the teeth is very variable. The extinct Theriodontia have teeth resembling incisors, canines, and molars. Grooved teeth occur in Ophidia, and in poisonous serpents the groove is well-developed in one tooth on each side and utilised to convey the secretion of the poison gland into the wound made by it. Somewhat similar but less specialised teeth occur in the poisonous lizard, Heloderma (Nature, xxvii. 1882-83: xxviii. 1883). A single large tooth implanted on the prae-maxillae serves to rupture the egg-shell in Lacerta and Anguis (Lacertilia) and in Tropidonotus (Ophidia). Salivary glands are absent in marine Chelonia, and the Alligator: they are confined to the tongue in the Crocodile, but, as a rule, there are not only lingual glands, but also sublingual, palatal, and labial.
A differentiation of one of the upper labials forms the poison gland of Ophidia. The tongue may be spatula-shaped and immobile, as in Chelonia and Crocodilia and some Lacertilia, or bifid, protrusible and more or less elongated as in other Reptilia. The oesophagus is wide and sometimes, as in Ophidia, not clearly marked off from the stomach. In marine Chelonia there are large papillae with points directed backwards towards the stomach. The cardiac portion of the latter is enlarged in the Crocodilia and shows on its flattened dorsal and ventral surfaces a tendinous spot whence the muscle fibres radiate; it is followed by a small pyloric enlargement. The small intestine is disposed in numerous coils in the Chelonia and Crocodilia. In the latter and in the Lacertilia it is non-glandular like the rest of the tract. The large intestine is short and straight, and it often has a small caecum close to the ileo-colic valve. It opens into a cloaca which has generally a dorsal enlargement, into which the urino-genital ducts open. The Chelonia have a pair of lateral bursae anales appended to the cloaca. And in the same group and the Lacertilia but in no other Reptilia a urinary bladder opens into it ventrally and anteriorly. The liver is bilobed as a rule.