168 Mr Houston on the Structure and Mechanism 



retractor muscles (Fig. 5, 1, 1.) arise, one from either side of the back part of 

 the annular muscle, and thence pass to its upper surface, where they meet 

 under the mucous gland, to be inserted into the bottom of the pouch. They 

 may contribute to the more effectual security of the prey, by deepening and 

 closing the pouch upon it, a change which this part evidently undergoes while 

 the organ is retiring into the mouth. 



To the second portion of the tongue I have given the name erectile, on ac- 

 count of the resemblance which I conceive it bears to the other erectile 

 structures of animals. It is placed between the prehensile portion and the 

 OS hyoides, and exhibits remarkable changes in bulk under different circum- 

 stances. When drawn from the mouth after death, which it may to the 

 length of five or six inches (Fig. 4, H), it presents itself as a slender chord, 

 so flexible and soft as scarcely to be felt when caught between the fingers, 

 and to appear little adapted for the purposes to which it is appUed. During 

 life, while the tongue rests in the mouth, this portion occupies an exceed- 

 ingly small space (Figs. 2, 7, H) ; but when projected in the pursuit of in- 

 sects, it becomes greatly increased in dimensions (Fig. 3, H), and appears to 

 be wholly the seat of that change which the organ undergoes in its elonga- 

 tion. Its structure is complex and peculiar. A fine transparent mucous 

 membrane, which is continuous posteriorly with that which lines the mouth 

 and throat, and anteriorly passes over the prehensile portion, encircles it on 

 all sides. The hyo-glossi muscles occupy its lateral surfaces. The}'^ are 

 round and thick posteriorly at their origin from the os hyoides, and become 

 thin and flat as they advance forwards to their insertion into the prehensile 

 portion. Their pale fibres are rendered evident by a dark vascular net-work 

 which is placed underneath them. Through the centre of the erectile portion 

 runs a tube (Fig. .5, p, p), which is attached behind to the style, and in front 

 is continuous with a similar structure already described in the prehensile 

 portion. It is soft, whitish, and homogeneous, of uniform size throughout, 

 and remarkably extensible. When the tongue is quiet in the mouth, the 

 tube lies folded on the style ; when advanced, it is drawn off" and elongated. 

 It follows all the motions of the organ, gliding with it alternately off" and on 

 the style, which is rounded and smooth for the purpose; but it cannot, as 

 some have supposed, take any part in causing the propulsion or retraction of 

 the tongue. A highly vascular structure exists between this tube and the 

 encircling mucous membrane, (Figs. 3, 4, 5, n, n). It extends from the root 

 of the style to the very end of the tongue, surrounding the tube equally on 

 all sides. Its vessels, which are rendered visible even to the naked eye by 

 their dark blood, appear, when examined with a magnifying glass, like a 

 beautiful trellis-work, the branches crossing and anastomosing with each 

 other to incalculable minuteness. A coloured spot, which resembles a mere 

 stain, exhibits through a glass a congeries of vetsels. This vascular appear- 

 ance has been described by the anatomists of the French Academy in the fol- 

 lowing words : " La membrane estait couvert de taches tout du long comme 

 si elle avoit este imbue ei dedans d'un sang noirastre, extravase et inegale- 

 ment amasse en plusieurs endroits." In another passage: "La langue 

 estoit semee de quantite de vaisseaux apparens a cause du sang qui y estoit 

 en grand abondance, ainsi que dans tout le reste du corps." But the circum- 



