A second looks forwards and outwards. This facet is smooth below,1 but is excavated above into a deep fossa, which in the fresh snake is partially closed by

PORTION OF CRANIUM OF CROTALUS.-Right side. Osteology. Bones concerned in the movements of the fang. a, external pterygoid bone; b, internal pterygoid bone; c, palatal bone; d, superior maxillary bone; e, lachrymal

bone.

soft tissues, but is still sufficiently remarkable as lying between the eye and nares. In the dry bone this large fossa opens upwards freely through the base of the bone, and thus separates the two surfaces by which the bone articulates with the ectopterygoid and lachrymal bones respectively. Anteriorly, the superior maxillary bone presents a rounded angle, from which diverge the two lateral sides just described. Posteriorly, the superior maxillary exhibits a third face, which is flat only half way down the bone, and terminates in an abrupt edge forming the posterior boundary of the alveolar socket.

Anteriorly, and above, the maxillary bone articulates by a ginglymoid joint with the short triangular lachrymal bone, Fig. 1, e, which projects forwards from the anterior external angle of the frontal bone. The articular facet of the maxilla lies at the upper end of its front angle. It moves with great freedom on the concave face of the lachrymal bone, its motion being partially restrained by a short, round, strong ligament, which runs from the posterior and inner edge of the lachrymal bone to be inserted on the back edge of the base of the maxilla, just above the articulation of the ecto-pterygoid bone.

The lachrymal bone has itself some movement on its frontal articulation, and by this the maxilla obtains indirectly an additional extent of forward motion. At the upper edge of the posterior surface of the maxillary bone, it receives the expanded and flattened end of the ecto-pterygoid bone, Fig. 1, a. Upon tracing the line of motion, of which this bone is capable, it will be seen that it lies below the lachrymal joint, and that, consequently, when it moves forwards, the fang must rise, as the superior maxillary rocks on the articulating face of the lachrymal bone.

The superior maxillary is indirectly attached to the palate bone, Fig. 1, c, and internal pterygoid, Fig. 1, b, by virtue of the strong connection of these bones with the ecto-pterygoid. This connection is so close that every free motion of either of

1 The parts are described as though in sitû.

the two former bones must inevitably affect the latter, and through it again the maxilla and its single tooth.'

The motion of the maxillary bone on its lachrymal articulation will, perhaps, be better understood upon reference to the accompanying diagram of the parts.

Diagram of the BONY PARTS CONCERNED IN RAISING THE FANG.-a, pterygoid bone; l, m, arrow marking its line of motion; p, e, pterygoideus externus muscle; g, frontal bone; d, lachrymal bone; c, superior maxillary bone; b, fang.

The myology of the subject is more complicated; yet even here our purpose will still be answered, if we describe only the muscles concerned, begging the reader to remember that all further details would be misplaced and useless. On reference to Fig. 3, it will be seen that the spheno-pterygoid, a, a strong muscle, arises along the raphe at the base of the cranium, and running backwards and outwards, is inserted fan-like upon the pterygoid plate. Acting from the fixed base of the skull upon the movable pterygoid bone, it must draw this bone forward, and, rocking the superior maxillary on its lachrymal joint, erect the fang, Fig. 2, l—m and arrow.

A second large muscle, the pterygoideus externus, Fig. 3, b, arises from the tough aponeurosis covering the zygomatico-mandibular articulation of the lower jaw, and as it runs forward below the poison gland and to its inner side sends a strong layer of white fascial tissue out upon the capsule of the gland. Some of its lower fibres are finally inserted directly into the two lips or edges of the mucous sheath of the tooth fang. A larger part of the muscle is inserted tendinously into an apophysis of the superior maxillary bone exteriorly to the articulation of that bone with the external pterygoid, and a little below it. The mechanical necessities arising from the position of this muscle are easily seen; for when the external pterygoid acts, it will necessarily depress the fang. This movement will be more readily comprehended on reference again to the diagram, Fig. 2, in the text, where p―e marks the line of action of the force applied by the pterygoid muscle to the superior maxillary bone and to the edges of the vagina dentis, the sheath of the fang. The action of this muscle is probably aided by the spheno-palatine, which arises along the raphe of the base of the skull, above the spheno-pterygoid and thus nearer the skull, and running diagonally outwards and backwards finds

1 These bones rest posteriorly against the articulation of the mandibule of the lower jaw with the zygoma; they consequently share, to some extent, in the movements of this joint.

insertion along the inside of the palatal bone. As its fibres cross those of the spheno-pterygoid, its action antagonizes that muscle and aids the purpose of the

MYOLOGY.-Palatal view of the muscles of the upper jaw and base of the skull. a, spheno-pterygoid muscle-the elevation of the fang is caused by its action on the pterygoid and palate bones; b, external pterygoid muscle-the retractor of the fang-inserted into the outside of the superior maxillary bone; c, fascial sheath of this muscle attached to the capsule of the venom gland; d, spheno-palatine muscle.

pterygoideus externus. The connection of the palate bone and the pterygoid bones, which we have already noticed, is essential to this result.

Almost all of the muscles about the head, neck, and jaws of the serpent, take part either in the motions which precede the blow, or those which inflict and follow it. Most of these muscles have functions which are obvious and easily demonstrable; and we shall, therefore, content ourselves with the briefest reference to all but the anterior temporal, which plays a far more important part, and requires a fuller description.

The mouth is opened by muscles, such as the costo-mandibular and the vertebromandibular, with the help of a muscular layer analogous to the platysma myoides. The articulation of the jaws is fixed by the double action of the digastricus and cervical angular muscles.

Of the temporal muscles there are three. The anterior temporal, Fig. 4, a, functionally the most important, arises from behind the orbit and from the upper

EXHIBITING THE RELATION OF THE TEMPORAL MUSCLES TO THE VENOM GLAND. a-a, anterior temporal muscle; b, its insertion in the lower jaw; c, venom gland; d, the fang half erected.

two-thirds of the firm fascia of the poison gland. Its fibres run backwards over this body and descend between it and the middle temporal muscle. In this course the fibres lie posteriorly to the suspensory ligament, and the outer ones, as they fold about the articular end of the gland, lie in contact with the prolongation of the external lateral articular ligament upon that body. Finally, the muscle winds around the commissure of the lips, and is inserted into the lower jaw some distance in front of the angle of the lips at b, Fig. 4.

The middle and posterior temporal muscles, Figs. 4 and 5, arise chiefly from the

MYOLOGY.-Lateral view. a-a, gland; b, anterior temporal muscle; c, posterior temporal muscle; d, digastricus muscle; e, posterior ligament of the sheath of the gland; f, vagina dentis-the fang slightly raised.

temporal fossa and are inserted, one behind the other, into the lower jaw. As these two latter muscles descend nearly vertically, their obvious function is to close the jaws. The use of the anterior temporal is in part also the closure of the jaws, but its more obvious office is to press upon the poison gland, as we shall presently see.

The poison gland of the Crotalus occupies the side of the head, behind the eye, and beneath the anterior temporal muscle, Fig. 5. Its posterior extremity extends three or four lines beyond the commissure of the lips. Its anterior end lies below and just behind the eye. Thus situated, the gland is in relation with the bony surface behind the eye, with the middle temporal muscle, with nerves which emerge under the suspensory ligament, and with the anterior temporal muscle above and behind, where that muscle descends to its insertion. Beneath, the gland is in contact with the external pterygoid muscle, with whose aponeurosis it has peculiar relations. So much of the gland as lies below the anterior temporal and above the line of the lip, is in relation with the skin which is here loosely connected with its fascia by areolar tissue.

The general form of the gland is that of a flattened, almond-shaped oval, the posterior end being somewhat obtuse, and the anterior tapering to the duct, which begins just behind and below the eyeball.

The length of the organ, from the insertion of the articular ligament to the beginning of the duct, was found to be eight-tenths of an inch, in a snake which was four feet long, and weighed two pounds and two ounces. Its breadth was nearly two-tenths of an inch, its thickness about one-eighth to one-tenth of an inch.

The poison-glands of six snakes were carefully weighed, after exhausting them of their contents, during the life of the snakes, and after the ducts and ligaments had been removed. In the following table, the weight of the gland, and the weight and length of the snake are given.

It is proper to mention that almost all of these snakes had been in captivity during periods of from two to eight weeks.

It will be seen from this table that very little relation can be established between the size and weight of the snake, and the weight of the gland, beyond the mere fact of the general increase in the size of the organ, with that of the snake.

The poison gland is invested with a double layer of white, and not very yielding fibrous tissue. The two layers of this membrane are united at the base of the gland, and becoming thinner anteriorly, they run off upon the duct, constituting a portion of its thickness. Besides furnishing attachment for the anterior temporal muscle, the outer layer of this capsule gives off three remarkable ligamentous expansions which suspend and confine the gland.

The posterior of these is a narrow, but strong ribbon of fibrous tissue, see Fig. 5, e, which runs from the posterior extremity of the gland to the articulation of the jaw, where it appears by its continuation backwards, to constitute one of the external ligaments of that joint.

The second, which we shall term the suspensory ligament, lies behind the gland,

A. THE GLAND AND TEMPORAL MUSCLES SEEN FROM ABOVE.-a, the gland; b, anterior temporal muscle; c, suspensory ligament of the gland extended; d, duct, drawn from its position.

B. DIAGRAM OF DUCT AND GLAND-SIDE VIEW.-a, the venom gland; b, the duct, at its curve; c, the sphincter; d, fang; e, superior maxillary bone.

Fig. 6 A, c, a little above its middle line. It arises as a fan-like expansion upon the capsule, and finally narrows to one-third, and is inserted on the bony surface