SNAKE-ROOT 



SNAKES 



529 



mountainous country, flowing through deep, lava- 

 walled canons, and is navigable for steamboats 

 only to Lewiston (160 miles). In Idaho its waters 

 are of value to the herds on the winter range. Its 

 chief affluents are the Boise, Owyhee, Malheur, 

 Salmon, Clearwater, and Palouse. 



Snake-root. See BISTORT, MILKWORTS, ARIS- 

 TOLOCHIA, and SENEGA. 



Snakes (Ophidia) form one of the classes of 

 reptiles, and are readily known by their shape, 

 being limbless and much elongated. To some 

 extent the shape may be an adaptation to the 

 habit of creeping through crevices and among 

 dense herbage ; for, apart from snakes, it is seen in 

 other animals which crawl through obstacles or 

 underground, in limbless lizards (e.g. Amphis- 

 b; i -iia and Anguis ), in the amphibian Ciecilians, in 

 various eel-like fishes, and in worms. 



General Habit and Structure. As regards habi- 

 tat we distinguish tree-snakes, usually green in 

 colour, of slender body, and of active habits ; the 

 water-snakes, including the non-poisonous fresh- 

 water forms, such as the British Grass Snake 

 and the tropical Anaconda, and the very venom- 

 ous sea-snakes (Hydrophidie), whose flattened tail, 

 apical nostrils, &c. are adaptations to their mode 

 of life; the burrowing snakes (Typhlopidae), with 

 rigid cylindrical bodies, narrow mouths, and no 

 specialised ventral shields ; and the majority, 

 which may be called ground-snakes. 



The scales covering the body are formed from 

 folds of skin. In each species of snake they 

 have a definite arrangement, which is greatly 

 relied on in the more detailed classification. 

 This is especially true of the shields on the 

 head, which are usually named after the under- 

 lying bones parietals, frontals, nasals, &c. ; thus 

 between the nasal scale (on which the nostril 

 opens) and the pre-orbital (in front of the eye) 

 there is in harmless snakes a loreal scale, which is 

 one of their characteristics. Most important in 

 the life of the animal are the strong ventral scales 

 or shields, for each of these is attached to a pair of 

 ribs and helps to grip the ground. As they corre- 

 spond in number to the vertebrse, they are also 

 diagnostic of species. The number of vertebrae in 

 snakes is often great, in some pythons amounting 

 to more than four hundred. They form a uniform 

 series, distinguishable only into pre-caudals and 

 caudals, and all the pre-caudals except the first 

 bear ribs. The bodies of the vertebne are con- 

 cave in front and have well-developed articular 

 processes. 



The skull is highly specialised. The bones which 

 form the brain-case proper are firmly united, but 

 most of the others are movable. Thus, ' when the 

 snake opens its mouth for the purpose of striking 

 its prey, the digastric muscle, pulling up the angle 

 of the mandible, at the same time thrusts the 

 distal end of the quadrate bone forward. This 

 necessitates the pushing forward of the pterygoid, 

 the result of which is twofold : firstly, the bending 

 of the pterygo-palatine joint ; secondly, the partial 

 rotation of" the maxillary upon its lachrymal joint, 

 the hinder end of the maxillary being thrust down- 

 ward and forward. In virtue of this rotation of 

 the maxillary, through about a quarter of a circle, 

 the dentigerous face of the maxilla looks down- 

 ward, and even a little forward, instead of back- 

 ward, and the fangs are erected in a vertical posi- 

 tion ' (Huxley). The halves of the lower jaw are 

 connected in front by an elastic ligament, and this, 

 combined with the "mobility of the quadrates and 

 squamosals, makes it possible for the snake to 

 swallow its relatively large prey. 



The teeth of snakes are short, conical, and sharp, 

 and are fused to the bones which bear them. The 

 460 



upper teeth may occur on the maxillae, palatines, 

 pterygoids, and rarely on the pre-maxillse ; the 

 lower teeth are borne as usual by the dentaries. 

 In the most venomous snakes, such as vipers and 

 rattlesnakes, the maxillary teeth are few, and each 

 is folded so as to form a tubular or grooved fang. 

 The specialised fang is connected by a gradual 

 series of forms with the ordinary teeth. 



As to the appendicular skeleton, no snake has any 

 trace of anterior limbs or girdle, and only a few 

 the pythons, boas, Typhlopida;, and Tortrices 

 have any rudiment of a pelvis. The pythons and 

 Tortrices have short rudiments of hind-limbs ter- 

 minated by claws. 



While the nervous system of snakes differs from 

 that of other reptiles only in small details, such as 

 the absence of a differentiated spinal accessory or 

 eleventh cranial nerve, the sense-organs are in 

 many respects peculiar. The eyelids, apparently 

 absent, are in reality fused as a transparent screen 

 in front of the eye, as is the case in Geckos and 

 some other lizards. The eyes are often very small, 

 and the sense of sight seems often to be dim. As 

 the common simile ' as deaf as an adder ' suggests, 

 the sense of hearing is also dull ; there is no exter- 

 nal ear and no tympanic cavity. The nostrils lie 

 at the apex of the snout ; the sense of smell seems 

 sufficiently acute to guide the snakes to their prey 

 and to their mates. In finding the latter they are 

 aided by the peculiar, sometimes musk-like odour 

 characteristic of snakes. Of a sense of taste they 

 have little need, for they swallow their prey whole, 

 nor are the usual gustatory organs present. It is 

 not too much to say that the most developed sense- 

 organ is the tactile tongue; with which snakes feel 

 their way and test everything which they touch. 



The internal structure of snakes presents several 

 peculiarities in adaptation to the elongated shape 

 of the body. Thus, the stomach is long but not 

 broad, the lobes of the liver are also elongated, 

 there is in most cases only one lung, the kidneys 

 are not opposite one another, and so on. The 

 elasticity of the food-canal is an adaptation to the 

 swallowing of relatively large booty, and during 

 this often slow process the larynx is shunted for- 

 ward into the mouth so that respiration is not 

 seriously impeded. Although boas, rattlesnakes, 

 and some others have paired lungs, most snakes 

 have only one, usually with a rudiment of the 

 other. There are often auxiliary air-sacs on the 

 windpipe, and the posterior part of the lung is 

 rather a reservoir for air than an actual breathing 

 organ. Apart from the characteristic hiss, pro- 

 duced by the forcible expulsion of air, most snakes 

 are dumb, but some boas are said to whine, and a 

 few others make peculiar sounds, of which the 

 rattling of the rattlesnakes is best known. In 

 having a three-chambered heart and a circulation 

 of mixed blood in the greater part of the body 

 snakes resemble lizards and tortoises. No urinary 

 bladder is developed. 



The Poison-apparatus. The poison-gland char- 

 acteristic of the venomous snakes is not a new 

 structure, but merely a specialised salivary gland, 

 and it is interesting to notice that a similar modi- 

 fication occurs in the poisonous Mexican lizard 

 Heloderma. From the gland, which lies on each 

 side behind the eye, and is about the size of an 

 almond in the cobra, a duct extends to the base of 

 the fang, down which the venomous juice flows 

 when the snake bites its victim. The fangs are 

 folded teeth, each an open groove, as in the sea- 

 snakes, or a closed tube, as in the vipers. It is of 

 course clearly to be understood that the ' sting of 

 the serpent ' is a poisonous bite. Stretching over 

 the poison-gland is the membranous origin of the 

 masseter muscle which works the lower jaw, and 

 by means of this and other somewhat complex 



