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Show 1890.] HELODERMA SUSPECTUM. 179 here. It arises from the anterior border of the leading cervical rib, and passing forwards and slightly inwards it is inserted into the side of the centrum of the atlas vertebra. The tendon of the levator scapulae of the same side is also attached there, just anterior to it. 63. Rectus posticus major.--Underlying the complexus, this muscle arises from the neurapophyses or neural spines of the first three or four cervical vertebrae, and passing directly forwards becomes inserted upon the posterior aspect of the cranium, into the supraoccipital bone. As the atlas is without neural spine, in its case the muscle only arises from the neurapophyses. 64. Rectus anticus major.-This is a very distinct and handsomely developed muscle ; arising from the ventral aspects of the first eight cervical vertebrae, or, more strictly speaking, from the ventral aspects of the centra of these vertebra?, and also from the anterior borders of the third to the fifth cervical ribs inclusive, it passes forward to insert itself into the basioccipital bone of the base of the cranium. Its points of origin from the ribs are to be found close to the vertebrae. 65. A small Scalenus anticus is to be seen arising from the lateral aspect of the second cervical vertebra, and the next one or two that follow it, and its fibres passing backwards and outwards are found to be inserted into the leading two free ribs of the neck, while internally it also attaches to the centra of the fifth and sixth vertebrae. Sanders has said of this muscle in Liolepis, that " at its insertion it is continuous dorsad with the sacro-lumbalis, and posteriorly with the intercostales." The same may be said of it in Heloderma. 66. The Caudal Muscles: the Supracaudal.-Structurally the tail of this reptile is quite a remarkable part of its organization, as the following description will go to show. It will be seen that it is naturally divided by four muscular sulci. Of these, one is a supero-median longitudinal sulcus, that, as in the case of all the others, runs the entire length of the tail: there are two mid-lateral sulci, one upon either side ; and, finally, an infero-median longitudinal sulcus. These grooves are carried clear down to the caudal vertebrae, each being lightly held together by connective tissue in life, except the superior one, in which feeble tendinous bands stretch across obliquely from side to side, that go to bind the supracaudals more closely together than any of the remaining tail-muscles. From this arrangement it will be seen that each lateral half of the tail has two divisions, a supero-lateral and an infero-lateral one. Each of these is made up of certain caudal muscles, which, beginning muscular at the body, become more and more fibro-tendinous as they proceed towards the tip of the tail. Upon making a transverse section of one of these parts, the fact is revealed to us that internally it is composed of two longitudinally disposed compartments, divided by the muscle dipping down between them. Either of these compartments is large and conically tipped at its proximal extremity, from whence it gradually tapers to a point at its distal end. The eight compartments of the tail, thus formed, are |
