A section made anterior to the free margin of this last-mentioned muscle, shows the cor tical portion continued completely round the tongue, without the break on its inferior sur face, occasioned, in the previous section, by the entrance of the genioglossi muscles ; it is also of greater thickness in proportion to the central part, which is comparatively small, and the transverse fibres have a less marked upward curvature at their extremities.
Thirdly, a section made near the base of the tongue shows the cortical portion nearly lost at the upper surface, greatly accumulated at the sides, but not of so compact a nature as in more anterior situations ; the obliquely ver tical fibres tolerably abundant, but the trans verse nearly lost, and the greater part of the inferior surface occupied by the expanded genioglossi.
Transverse vertical sections, therefore, dis play two sets of fibres, a vertical and a trans verse, and shew their situation and quantity; let us now see what additional light will be fur nished by a longitudinal vertical section. It shews that the cortical portion consists of lon gitudinal fibres, and thus supplies a third set. If the section be made in the middle line, or near it, the whole cut surface is occupied by the vertical fibres of the geniohyoglossus, at first directed backwards, but curving upwards so as to enter the tongue vertically, in which vertical direction they are continued up through its entire thickness, and are lost in the longi tudinal fibres of the cortical portion ; if the section is made in the lateral portions, it shows the vertical striation occasioned by the in trinsic vertical fibres, and the cortical portion, as in the other. Having ascertained the si tuation and direction of the three sorts of fibres, we may, by making transverse sections at all points from the apex to the base, and longitudinal ones at various distances from the vertical median plane, and also by tracing the extrinsic longitudinal muscles into the intrinsic, and seeing what part of the one the other fur nishes, get an exact interpretation of them. We should then find the tongue to consist of the following muscles.
a. A transverse altogether intrinsic, inserted on each side into the submucous fibrous tissue or cutis, continued from apex to base, more abundant anteriorly, where it is horizontal, becoming more curved upwards as we proceed backwards, and being lost at the base.
/3. A vertical lingual, in part intrinsic ; in part the lingual portion of an extrinsic muscle, the genioglossus, existing from apex to base, in all parts vertical to the surface, and there fore, from the curved direction of the tongue, arranged in a more or less radiating or fan like manner.
•y . A superior lingual, longitudinal, in trinsic, thin behind, thicker in the middle, and thinner again at the apex, arising from the hyoglossal membrane and cutis at the base of the tongue in a gradual way, and having a similar cutaneous insertion on the upper surface of the tip and neighbouring parts.
S. A lateral lingual, longitudinal, altogether extrinsic in its origin ; derived from two prin cipal sources ; one, its upper and most super ficial portion from the fibres of the stylo glossus, which pass forward on the side of the tongue after the insertion of that muscle into it, the other from the anterior fibres of the hyoglossus which have a similar distribution : to this may be added a slender fasciculus of fibres interposed between the styloglossus and hyoglossus, which many modern anatomists* have described as the lingual muscle. The muscle thus formed constitutes the accumula tion of longitudinal fibres before referred to as seen at the sides of a transverse vertical section of the base ; passing forwards they become fused together and spread out so as to constitute a thin layer, merging above by converging towards the medial plane of the dorsum, in the superior lingual, below in that next to be described, and forming with them a sheath of longitudinal fibres, investing the whole surface of the tongue.
E. An inferior lingual, a stout fasciculus of longitudinal muscular fibres entirely intrinsic, arising at the base of the tongue between the hyoglossus and genioglossus, and passing forwards between these two muscles to be inserted gradually into the cutis of the tongue on the inferior surface near the apex. This is the true lingual muscle of Douglas and Al binus, and of anatomists of the present day. I am doubtful whether or not the most an terior fibres of the genioglossus bend for wards so much as to become longitudinal, but I think not (though Cruveilhier says they do): if they do, the longitudinal sheath in front of the free margin of the genioglossus would consist of four sets, behind it of three.