230 ANATOMY OF VERTEBRATES. 



the modification of the bones peculiar to venomous serpents, as 

 shown at 3 and 2, fig. 146, the muscle rotates the short maxillary 

 vertically through the ectopterygoid, so as to bring the venom- 

 fang from the recumbent to the vertical position ready for the 

 blow. 



The presphenopalatine muscle arises from the side of the fore 

 part of the presphenoid and passes outward to its insertion along 

 the inner surface of the palatine. From the side of the pre- 

 sphenoid rises the small presplieno-vomerine muscle, fig. 146, v, 

 which sends forward a slender tendon to the half of the divided 

 vomer, and through that bone depresses and retracts the pre- 

 maxillary, ib. l, after the displacement of all the bones of the 

 mouth caused by the engulphing of the prey. 



The hyoid arch is reduced to a pair of slender cartilaginous 

 ceratohyals, running forward, almost parallel, fig. 147, B, beneath 

 the sheath of the filamentary tongue, before their anterior mem- 

 branous union. The raphe of the muscles v and u, fig. 147, is so 

 far attached to the hyoid and lingual sheath, that by their con- 

 traction they raise the tongue after it has been pushed down : the 

 fibres of the costomandibularis, u, attached to the foremost part of 

 the mandible, through the same medial attachment protract the 

 lingual sheath ; the posterior part of the costomandibularis can 

 retract the lingual sheath, and these actions are analogous to those 

 of the ' sternohyoid ' and ' geniohyoid ' muscles in higher verte- 

 brates. On reflecting the costomandibularis from the raphe out- 

 ward, the genioglossi are exposed : their antero-median attachment, 

 fig. 147, z', zf , is to the raphe of the intermandibularis, v ; their 

 antero-lateral attachment, z // , is to the fore end of the mandibular 

 ramus. The muscle formed by their union, z, extends backward 

 along the lingual sheath to its extremity : it is the chief pro- 

 truder of the tongue. The retractors, answering to hyoglossi, 

 ib. A, arise from the hinder ends of the ceratohyals, run forward, 

 enter the lingual sheath, and seem to coalesce in forming the 

 main substance of the cylindrical tongue ; but they again separate 

 to terminate in its forked extremity. The fore part of the trachea 

 is closely connected with the lingual sheath, and advances so far 

 forward to terminate in the mouth, as to be subject to the stretch- 

 ings and displacements of the elastic floor of that cavity. A 

 special muscle, geniotrachealis, fig. 147, y, arises from the fore 

 end of the mandibular ramus, and passes inward and backward 

 to expand upon the sides of the fore part of the trachea. The 

 pair draw forward the glottis ; its retraction is effected through 

 the medium of the lingual sheath and its muscles. 



