caudal vertebræ have both a hæmal and a neural arch. The thorax is composed of a sternum and two sets of ribs, viz., dorsal and sternal, connected together by cartilage. The anterior portion of the sternum is osseous, but posteriorly it becomes cartilaginous, and is prolonged as far as the pubis, on each side giving attachment to eight abdominal ribs, supposed to be represented in man by the tendinous intersection of the rectus abdominis muscle; there are no clavicles. All four limbs are present, the anterior being provided with five toes, the posterior with four. The mouth is large, and, in addition to the conical teeth already described, contains a large, fleshy, movable tongue. The orifice leading from the mouth into the pharynx and larynx can be closed by means of a strong valvular apparatus, formed by a prolongation of the soft palate, and a muscular membranous expansion arising to meet this from the hyoid bone; and as the nostrils open at the extremity of the mouth by a single aperture, the crocodile is able, without any inconvenience, to hold his prey under water, the nostrils opening into the pharynx behind this valvular septum. The æsophagus is short, and leads into a strong gizzard-like stomach, which often contains stones to assist in the proper trituration of food.* The pyloric opening, guarded by a valve, is situated near the cardiac extremity, and leads into a short intestine, which terminates in a common cloaca, the aperture of which is longitudinal. The heart consists of four distinct chambers, as the ventricular septum is complete, but nevertheless the arterial and venous blood always communicate through the "foramen of Panizza,” which is situated between the pulmonary artery and aorta, immediately after their origin. The eyes possess the same tunics and humours as in man, and are guarded by three eyelids.

* Professor Haughton found several flint stones in an alligator which he dissected.

The ear consists of a vestibule, three semi-circular canals, a rudimentary cochlea; a middle ear, containing three ossicles, a membrana tympani, and a movable ear-lid. The body is covered by a layer of horny epidermic scales, resting on a dermal skeleton of bony plates or scutes, which may be present only on the dorsal aspect, or may exist on the ventral as well. This order is divided by Professor Owen into the following sub-orders :

a. Procælia (pó, in front; and коíλos, hollow).—Recent.

b. Amphicælia (aupt, on both sides; and kolhos)} Extinct.

c. Opisthocælia (ŏπσ0e, behind; and koíλos)

Procælia contain all the existing members of the crocodilia, and are divided into

1. Gavial (India), having a long snout, and numerous even teeth.

2. Crocodile (Nile), having a long obtuse snout, and the fourth tooth in the upper jaw large and visible.

3. Crocodile vel Alligator (America), having a broad snout, and the fourth tooth in lower jaw large and concealed.

II. LACERTILIA.-All the members of this order are distinguished by the following characters:-The majority of them have four limbs, a few have only two, while some have none; all, however, possess a scapular arch; movable eyelids are generally present in the snake-like forms always so—thus at once distinguishing this order from the ophidia. The dorsal vertebræ are generally procælous, rarely amphicælous; there is a single transverse process, and the heads of the ribs are simple; there is no sacrum. The teeth are never implanted in distinct sockets. The heart consists of two auricles, and a single ventricle, which is incompletely divided by a septum. The aperture of the cloaca is trans

verse. An exoskeleton, composed of horny epidermic scales, is almost always present. This order includes the Lizards, Chamæleons, Iguanas, Geckoes, and Slow-worms.

1. Lizards (lacertidae). This group comprises the typical lizards. They have two pair of well-developed limbs, each furnished with five toes of unequal length. The body is covered with scales, which are developed into shields or "scuta" over the abdomen and on the head; the tail is rounded; the tongue is slender, bifid, and protrusible. This family includes the sand-lizard (lacerta agilis), the viviparous lizard (zootoca vivipara), and the green lizard (lacerta viridis). Closely allied to the true lizards are the monitors (varanidæ), in which the abdomen and head are covered with scales instead of "scuta "-these are the largest of all existing lizards, some attaining the length of from six to eight feet.

2. Chamæleons are easily distinguished from the other members of this order by their peculiar tongue, which is long, fleshy, round, glutinous, and exsertile (exsertus, thrust out); they can project it at a fly with extraordinary rapidity. Their tail is prehensile; both eyelids unite to form a single circular eyelid, having an aperture in the centre. They are also remarkable for possessing the power of changing their colour.

3. Iguanas are known by their tongue, which is thick, fleshy, notched at its extremity, and non-protrusible_ besides, there are generally present a dorsal crest and throat pouch (goitre). The body is covered with imbricated scales. They are sometimes divided into "ground iguanas," having a flattened head and depressed body, and "tree iguanas," in which the body is compressed laterally. It is stated that they can sometimes be tamed. Allied to the iguanas are the singular lizards called “flying dragons;" they are small, arboreal in their habits, and live upon insects. The anterior

ribs are strangely modified, inasmuch as they pass straight out from the spinal column, and support an expansion of the integument, which acts as a parachute, thus allowing the animal to take extensive leaps.

4. Geckoes, so called from the peculiar sound they utter, are nocturnal in their habits. They do not possess movable eyelids, but the eyes move freely behind a transparent fixed eyelid. Their toes are on each side provided with a leaflike expansion, hence they can climb even vertical surfaces, or walk along the ceiling; it is supposed that this mechanism causes the toes to act as small suckers, and that the body is supported by atmospheric pressure when they walk along a ceiling; the toes are also sometimes furnished with retractile claws.

5. Slow-worms (blind-worms) are very snake-like in their external appearance, as they possess no limbs. The scapular and pelvic arches are, however, always present in a rudimentary condition; the eyes are provided with movable eyelids, having a longitudinal slit. When frightened, they can stiffen their muscles to such an extent that the tail çan readily be broken off, as if it were brittle—hence they are called "angues fragiles." They are harmless, and live upon insects, slugs, &c., and remain under ground during the winter in a state of torpor.

III. OPHIDIA.—This order comprises all the snakes and serpents; they are true reptiles, as they possess no limbs whatever, and are known by the following characters :— The body is elongated, cylindrical, and covered with a scaly epidermic investment (there is never a bony exoskeleton present), which is generally shed in one piece, and reproduced at definite periods. In the rattle-snake this epidermic covering becomes modified at the extremity of the tail, and forms the rattle, which is composed of several

horny rings, loosely joined together. The number of vertebræ in the spinal column is considerable (amounting in some of the large pythons to more than four hundred), divided into caudal and præcaudal regions, there being no sacrum; the dorsal vertebræ are procælous, and have rudimentary transverse processes. The sternum, scapular arch, and fore-limbs are always absent, and, as a rule, there are no traces of the hind limbs-rudimentary hind limbs are, however, represented in the pythons by a few imperfectly developed bones situated on each side of the anal vent in the muscles of the abdomen, which, when they project externally, are called "claws" or "spurs" (calcaria). The two rami of the lower jaw are composed of several pieces, united in front by ligaments and muscles only; the os quadratum is movable, and so are the mastoid and tympanic elements of the temporal bone; the maxillæ are united to the præmaxilla by muscles and ligaments, and the arches of the palate are also movable. In consequence of this great mobility of all the bones surrounding the oral aperture, the ophidian reptiles are enabled to open their mouths to an enormous extent, and swallow their prey whole. The teeth in these animals are never placed in sockets, but are firmly anchylosed to the jaws; they are curved inwards, and are never used in mastication, but are simply employed in seizing and holding their prey. A very curious and interesting modification of the reptilian dental system occurs in the venomous snakes, where there are two poison-fangs united by movable joints to the superior maxillary bones, and communicating with the duct of a poison-gland, which is situated under and behind the eye. Each poison-fang is formed by a flexion inwards of a simple slender tooth (Owen), so as to form a tube, the opening of which is near the apex of the fang; when not in action, the fang lies in the gum pointed backwards, but, when its owner is about to bite, it is raised from the gum and pointed downwards—

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