1890.] HELODKRiVIA 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 

 scapula 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 vertebrae, 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 vertebr£e. 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 Supracuudal. — 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 longitu- 

 dinal 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 obUquely 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 



