The following points of anatomy may be noted, not visible in the specimen. The subcutaneous connective tissue is very scanty in amount and absent altogether on the abdominal surface.

Nervous System

The olfactory lobes of the brain are swollen terminally and are long; the prosencephala broad; the cerebellum somewhat tongue-shaped and projecting over the fourth ventricle. The pituitary body is broad. The parts of the brain lie nearly all in one plane. There is no spinal accessory nerve.

Special Sense Organs

There is no tympanic cavity. Among Lizards, the Geckoes (Ascalabota) Amphisbaenae and some others resemble the Ophidia in the fusion of the eye-lids. There is thus formed a lacrymal sinus.

Circulatory Organs

There is a sinus venosus formed by the union of the vena cava inferior and the right jugular vein. It opens into the right auricle by an aperture guarded by two valves. The left jugular opens into the auricle separately. A single pulmonary vein opens into the left auricle. The two auricles are separated by a septum, the free edge of which is produced into a right and left auriculo-ventricular valve. The ventricle has a single cavity partially subdivided by a muscular band or septum on its anterior wall. To the right of this septum is the cavum pulmonale from which the pulmonary artery arises. The left side of the ventricular cavity is divisible in turn into a left cavum arteriosum into which the left auricle opens and a right cavum venosum from which arise to the right the left aorta, to the left the right aorta. Hence these two vessels cross at their origins. In contraction of the heart the septum isolates the cavum pulmonale completely. The three great vessels, i. e. two aortae and pulmonary artery have, as in all Reptilia, two semilunar valves at their origin.

In the arterial system the right aorta gives off, first, two coronary arteries; secondly, an arteria cephalica, the common origin of the two carotids; thirdly, an arteria collaris, which runs beneath the back-bone and ends close to the head. The left aorta gives off no branches. The subvertebral aorta has no caeliac axis; there are several hepatic and renal arteries, and the right and left intercostal arteries arise by a common stem. The aorta is continued into the tail as the caudal artery. The pulmonary vein lies hidden by the vena cava.

In the venous system, the right inferior jugular close to the heart receives two veins, a short anterior and a long posterior azygos. The vena cava inferior is formed by the union of the two efferent renal veins; it receives the ovarian (or testicular) veins, and the hepatic veins in its course along the liver. The portal vein rises on the dorsal wall of the cloaca and receives the veins of the intestines, stomach, spleen, pancreas, the epigastric vein and the intercostal veins. It runs on the visceral surface of the liver to which it is distributed. The reni-portal veins of the kidneys are formed by the bifurcation of the caudal vein. There are anastomoses between them, the portal, and the epigastric veins.

Digestive System

The tongue is partially contained in a sheath which opens anteriorly on the floor of the mouth. Leydig describes a paired and an azygos gland in connection with this sheath. The stomach gradually contracts to the pylorus, which is well developed. The last six inches of the small intestine are nearly straight; it opens laterally into the large intestine, and there is in some specimens a short caecum (as in the Pythons) at this spot. The large intestine is about three and a half inches long; it gradually increases in calibre to the cloaca, from which it is marked off by a constriction.

Respiratory System

The posterior portion of the lung is thin and not alved-lated, and receives blood from the hepatic arteries. In Pythons the left lung is functional, though smaller than the right, In Hydrophis cyanocincta - a marine serpent - the lung extends to the cloaca, beneath the back-bone.

Urinary System

The ureter runs centrally between the reni-portal vein on the outer and the efferent renal vein on the inner side. There is no urinary bladder.

Generative Organs

The testes are elongate, rounded organs with a small epididymis, and placed asymmetrically like the ovaries. The vas deferens is thrown into short coils and accompanies the ureter of its own side, and opens finally into the terminal dilatation of the ureter, in which spermatozoa are found at the breeding season. Each ureter opens on a dorsal papilla in the cloaca; and a groove leads from it to the apertures of the intromittent sacs. These are eversible, and their inner surfaces are clothed with epidermic spines. They are retracted by muscles.

The right is often larger than the left ovary. The oviduct has a large ostium with an entire margin as in all Vertebrata, save Mammalia. The two oviducts fuse into a short vagina, which opens dorsally into the cloaca near its outlet. The two ureters open on a dorsal papilla quite close to the same outlet. The post-cloacal sacs of the female are smooth and non-eversible.

Note on the poison glands.The white gland mentioned above in the English Grass-snake becomes much enlarged in those colubriform snakes in which one or more of the posterior maxillary teeth are grooved. Such serpents were termed Opisthoglypha by Bibron and Dumeril, Ophidia suspecta by Schlegel. But a serpent with furrowed teeth may be found in the same family as a serpent with none but solid teeth, e. g. Homalocranion with grooved and Calamaria with solid teeth in the family Calamaridae. Hence the terms have been abandoned as of no classificatory value. The members of certain families, however, among the colubriform snakes are always opisthoglyph, e.g. Psammophidae, Dipsadidae, and some of them appear to be undoubtedly poisonous.

The serpents belonging to the suborders, Proteroglypha and Solenoglypha, are all venomous in the highest degree. In the former there is a large furrowed tooth at the anterior end of the maxilla, and behind it a series of small solid teeth: in the latter the maxilla is much reduced, very moveable, and provided with but a single large furrowed tooth and the germs of its successors. The Proteroglypha include the Elapidae, e.g. the Cobra di Capello (Naja tripudians) and the marine Hydrophidae; the Solenoglypha, the Viperidae, e. g. the English Viper (Pelias), and the Crotalidae, e.g. the Rattlesnake (Crotalus horridus). In both these sub-orders the white gland (supra) reaches its maximum of development. The ligamentum zygomaticum ( = an unossified jugal) which stretches internally to the gland between the maxilla and the quadrate, develops a silvery fascia-like pouch enclosing the gland. One of the three divisions of the temporal muscle is attached to the internal aspect of this pouch: and from its posterior end the masseter takes its origin and passes down to the mandible.

The gland is also enclosed in a tough fibrous investment of its own Within this investment there is in Pelias berus loose connective tissue with large lymphatic spaces said to be absent in Naja haje (Emery). The gland tubes are united together by a fibrous coat with which the loose investment is continuous. The tubes are collected into bundles, and open into a single duct. This duct opens above the base of the furrowed tooth, and a fold of the mucous membrane surrounds both the base of the tooth and the aperture of the duct. Hence the poison flows down the channel of the tooth, when the contraction of the muscles attached to the outermost capsule forcibly ejects it in the act of closing the jaw. The poison is not only secreted in the gland tubes, but is likewise stored within them. The quantity ejected is large at the first bite, but becomes less and less with successive bites. In Elaps (? all species) the poison glands are much elongated, and reach far down the body. As a rule they do not extend beyond the angle of the jaw.

Reptilia, Hoffmann, Bronn's Klass. und Ordn. des Thierreichs, vi. Abth. 3. Erpetologie generale, Dumeril and Bibron, 9 vols. Paris, 1834-54. Reptiles of British India, Gunther, Ray Soc. 1861. Thanatophidia of India, Fayrer, 1874.

Natrix. Bell, British Reptiles. London, 1839, p. 47.

Integument with sense organs.Leydig, A. M. A. viii. 1872; ix. 1873. Todaro, Atti dell' Academia dei Lyncei (3), ii. part 2, 1878 (Math. Nat. Class). Merkel, Endigungen der sensibeln Nerven, Rostock, 1880. Cf. Knauer, Z. A. ii. 1879.

Organs of circulation.Jacquart, A. Sc. N. (4) iv. 1855. Briicke, Dk. Akad. Wien, iii. 1852. Rathke, ibid. xi. part 2, 1856. Heart. Sabatier, Etudes sur le Coeur, Paris, 1873. Renal-portal System. Jourdain, A. Sc. N. (4) xii. 1859.

Organs of respiration.Milne-Edwards, Lecons sur la Physiologie, etc. ii. 1857; Schulze, Strieker's Histology, (Sydenham Soc.) ii. 1872.

Organs of digestion.Teeth. Tomes, Ph. Tr. 165, 1875: Leydig, A. M. A. ix. 1873; Gervais, Journal de Zoologie, ii. 1873. Glands, Leydig, A. M. A. ix. 1873; Meyer, Monatsberichte, Akad. Berlin, 1869; Emery, A. M. A. xi. 1875; Reichel, M. J. viii. 1882; Digestive tract, spleen, etc, Duvernoy, A. Sc. N. 26, 1832; 30, 1833. Stomach, Edinger, A. M. A. xvii. 1880.

Excretory organs and genitalia.Braun, Arb. Zool. Zoot. Inst. Wurzburg, iv. 1877-78. Supra-renals. Id. op. cit. v. 1882.

Reproductive organs.Martin Saint-Ange, Etudes de l'appareil Reproducteur des Animaux Vertdbre's, Paris, 1854 (Mem. par divers savants, Academie des Sciences, xiv. 1856).