Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/475

MUSCLES.] REPTILES 457 their tendons and much connexion with other muscles in the popliteal space. The Crocodilia have an adductor femoris, which arises from beneath the transverse processes of the lumbar region and is inserted by a broad tendon into the femur. An iliacus arises from the inner side of the ilium and ischium, and goes to the inner side of the femur. Several adductors proceed to the femur from the ischium. A long muscle arises from the chevron bones and transverse pro- cesses of the anterior third of the tail, and is inserted by a strong tendon into the trochanter ; thence descends another tendon along the flexor side of the femur to join the tendon of origin of the gastrocnemius, which springs from the external condyle. The Chelonia possess an abductor femoris, which passes from beneath the transverse processes of the thoracic vertebrae, and also a sort of psoas extending from their transverse processes to the ilium. Another muscle goes from the hindmost thoracic transverse processes to the femur. A muscle, attrahens pelvim, arises from within the plastron and goes to the outer process of the pubis. Another muscle which antagonizes this, the retrahens pelvim, springs from the hindermost part of the plastron and goes to the pubis. Other retractors pass from the caudal chevron bones to the front border of the obturator foramen, and another muscle with a similar origin is inserted into the ischial symphysis. The muscles of the more distal part of the limb are less peculiar, and need not be described here. ^ The Alimentary System. All Reptiles agree in having an alimentary tract which begins with jaws armed mostly with teeth, rarely with horny sheaths, but never in existing Reptiles with both, though (as has been elsewhere described) such a combination is found in some fossil forms. Moreover, teeth are mostly found not only at the margins of the jaws but also on the palate. Almost always there is a tongue, and glandular structures around the mouth pour their secretion into that cavity, which communicates, by tubular prolongation, with the ears, the eyes, and the nostrils. The mouth opens posteriorly into the commencement of a more or less prolonged ali- mentary canal, the anterior part of which is not, while the greater and less posterior part is, embraced by the peri- toneum. At its hinder end this canal opens into a chamber called the cloaca, into which the urinary and generative ducts also open, and which itself opens beneath the hinder part of the trunk by a roundish longitudinal or transversely extended aperture. Two accessory glands aid digestion by the products they pour into the canal. These are the pancreas and the liver, and the latter is always provided with a gall-bladder. A spleen is also always found in the vicinity of the stomach or specially digestive dilatation of the alimentary canal towards its anterior end and separated from the mouth only by the oesophagus. Oplii- The several main groups of existing Reptiles present the ins > following characters : The Ophulia all possess teeth, mostly well developed and anchylosed to the bones which support them. By rare excep- tion, as in DasypeUis scaber, the teeth may be quite minute, the hypapophyses of the anterior trunk vertebra penetrating the dorsal wall of the alimentary canal and being tipped with tooth substance, and taking the place of teeth, as already mentioned in describ- ing the axial skeleton. Teeth generally exist on the palatines and pterygoids as well as on the maxillse and mandible, and in Python and Tortrix in the premaxilla. They may bo absent from the palate, as in Uropdtis. But the various conditions as to the dis- position of the teeth have already been given in the systematic part of this article. In the majority of Serpents the teeth are solid or have but their pulp cavity, but in some harmless ones one or more of the hind- most teeth which are set on the maxilla are longitudinally grooved along their convex side. In poisonous Serpents each maxilla supports a poison fang or tooth so deeply grooved that the margins of the groove meet and so convert the grooved tract into a canal, down which the duct of a poison gland passes. This fang may be the only functional maxillary tooth, as in Crotalus and Vipera, or there may be other teeth behind it, also grooved, as in Naja, or entire, as in Bungarus. Almost all Ophidians have a row of small labial salivary glands along either margin of each jaw, their secretion escaping into the mouth by numerous small apertures. In addition to this, some apparently innocuous snakes with grooved teeth have an additional glandular mass connected with the upper labial gland and pouring its secretion by a duct into the dental groove. The truly poisonous Serpents possess a gland placed above the maxilla and os transversum and beneath and behind the ball of the eye, and of different size and extent in different genera. In Naja it may extend for about one-sixth the length of the body, but in Callaphis 1 it may be yet greater and extend throughout nearly half the length of the entire body of the animal. The poison gland has a fibrous investment, which is often contractile from the presence in it of muscular fibres, and often jaw muscles are so arranged (as already mentioned) as to exert pressure on the gland by their contraction. A nasal gland and a lachrymal gland also convey their secretion into the mouth. The tongue is long, bifurcated anteriorly, and extremely mobile, being capable of protrusion from and retraction into a membranous sheath, placed on the floor of the mouth beneath the ventral wall of the larynx. The oesophagus is long. The stomach begins by a well-defined limit beside the liver, and may or may not form a curve, but is always simple. A valve at its pyloric end marks the commencement of the duodenum. The small intestine varies much as to the number of its convolutions, which are connected by bands of fibrous tissue and are not followed by foldings of the mesentery. A circular protuber- ance generally marks its junction with the shorter large intestine, and sometimes there is a caicum, as in Typhlops, 2'ortrix, Python, and others. The large intestine may be simple, and its internal cavity may be augmented by valves or partial partitions. The cloaca opens externally by a transverse aperture. The liver is not sub- divided into conspicuous lobes. The gall-bladder lies separate from the liver and posterior to it. The ductus choledochus passes through the pancreas, which lies behind the pylorus at the right side of the duodenum and is pyramidal (or rounded), or compact, or in separate parts, as in Hydrophis. The spleen lies immediately behind the pancreas. It is rounded, small, and generally entire, not lobed. The Lacertilia all possess teeth along the margins of the jaws in Lacei and very often in the palatines also ; but it is only by rare tilians ; exception, as, e.g., in Iguana, that the pterygoids bear teeth. In the Chamseleons the teeth are very rudimentary, little more than an enamelled dentated ridge on the margin of either jaw. The teeth of most Saurians are either acrodont, i.e., anchylosed to the free margins of the jaws (as, e.g., in Psammosaurus), or pleuro- dont, i.e., anchylosed to the inner side of the jaws, their crowns projecting above the margin (as, e.g., in Iguana). Generally more or less conical, the teeth may be acutely pointed, or extremely obtuse, as the hinder teeth of Cydodus. Sometimes, as, e.g. , in Iguana, the teeth may be compressed with a median external vertical ridge and a serrated margin. By rare exception, as, e.g., in Chlamydosaurus, the teetli of either jaw may be much dif- ferentiated. Here we have a simulation, or anticipation, of that division of the teeth into incisors, canines, and molars which is so general in the class Mammalia. 2 In the genus Heloderma the teeth are vertically grooved so as to remind us of their structure in Serpents. The teeth indeed are more grooved than in them, for one vertical groove passes down on the antero-inner side and another on the postero-outer side of each tooth. Labial salivary glands generally exist, but are small. In Hdodcrma, however, and in no other known Lizard, there is a very large salivary gland on either side of the lower jaw. The quality of its saliva is distinctly poisonous, small animals bitten by Heloderma in our zoological gardens dying as if bitten by a venomous Serpent. No other such case is known to exist amongst the Lacertilia. The tongue presents a number of variations of form which have been already referred to as diagnostic characters in the systematic part of this article. It will suffice here to remind the reader that it may be broad and fiat without any sheath, and with a pair of anterior and of posterior processes, as in Arnphisbsena ; or short, broad, and slightly notched in front, as in Gecko ; or short with a slight bifurcation in front and two long processes behind, as in CJialcis ; or with a sheath, and much like that of Serpents, as in Psammosaurus ; or cylindrical and wonderfully extensile, as in Chameeleo. The oesophagus passes into a stomach, which is generally elon- gated and curved. The small intestine may be hardly at all convoluted (as in Amphisbasna) or very much so, but if so the mesentery here follows its folds. Similarly the large intestine may be short and straight, or long and with internal folds. There may be a caecum, as, e.g., in AmphisbtKna and some Chamaeleons. The cloaca opens externally by a transverse aperture. The liver is but little lobed, and its gall-bladder lies in a fissure on its left side. The pancreas and spleen usually lie between the folds of the mesentery at the junction of the small intestine with the stomach. There is generally a pair of anal glands. In Hatteria the large teeth in the premaxillse become completely in Hat- anchylosed with those bones, reminding us of the extinct JRhyncho- teria ; saurus and Hyperodapedon. Most of the teeth which lie along the 1 See A. B. Meyer, Monatsb. der Akad. d. Wissen. z. Berlin, 1869. 2 This fact thus affords an interesting illustration of the independent origin of similar structures. XX. 58