OF REPTILES AND BIRDS. 5 



extend behind the point a, where the tongue and sheath unite. Three pairs of nerves 

 enter the tongue, each being accompanied by an artery. The first, A, goes to the sheath 

 a short distance in front of the attaclirnent, a, of the tongue ; the second, B, enters 

 about the same distance behind the attachment as the nerve A before it. The third, C, 

 enters about half way between the point, a, and the posterior extremity of the tongue. 

 Its point of entry marks a division line in front of which the tongue has both longi- 

 tudinal and transverse muscles, fig. 10, and back of which it has only longitudinal fibres, 

 fig. 11. In the latter region the fibres form two distinct bundles, separated at first by 

 slight depressions above and below, which deepen posteriorly until they finally meet, 

 forming a fissure, which divides the two muscles, c. gl., the cerato-glossi, one for each 

 hyoid cornu. 



The upper half of the free portion of the tongue is somewhat expanded, and is marked 

 off from the lower surface by a shallow longitudinal furrow on either side of the tongue. 

 These furrows face downward, and extend from the level of the fork half way or more 

 to the point of attachment. 



When the tongue is extended, the point of attachment moves forwards, and the free 

 part of the tongue lengthens. It is probable that, when the tongue is retracted, the 

 nerves are thrown into sinuosities, which are straightened out when the tongue is 

 exserted. This disposition occurs in other nerves in snakes, to allow for the distension of 

 the part, because the nerve-tubes, not being elastic, would be injured by stretching. 



In the Ophidia, as is well known, the hyoidean apparatus of cartilages and bones is 

 reduced to a single cartilaginous piece, consisting of a thicker median part often with 

 an anterior spine, and of two unusiially long thread-like cornua, to which the ceratoglossal 

 muscles are attached. In the amniote vertebrates, and also in the Amphibia, there are 

 usually numerous distinct muscles differentiated in the intermandibular area. Of these 

 muscles, the mylo-hyoid, genio-hyoid, genio-glossus, sterno-hyoid, omo-hyoid, and costo- 

 hyoid are the most constant, but in the snakes they are all fused to form a single 

 uninterrupted layer. Duges, it is true, figures and describes several distinct muscles, 

 but Duvernoy (v) who makes no mention of Duges' earlier paper, found a single layer, 

 extending from the transverse processes of four or five of the anterior vertebrae, and from 

 the anterior ribs, downwards over the whole intermandibular region. Dumeril and 

 Jacquart (iv) state that the fibres from the ribs are continuous with M. ohliqims 

 internus ; they figure (iv, plate 20, fig. 2, and plate 21, fig. 3) that connection in the 

 boa. My own observations entirely agree with those of Duvernoy. The layer is quite 

 thin, and separated from the ectoderm by the dermis only. Its fibres run, 1, transversely 

 between the anterior ends of the mandibles ; 2, from near the anterior ends of the mandi- 

 bles to the hyoid cartilage ; 3, from the hyoid to the ribs and vertebrae ; 4, from the pos- 

 terior portion of the mandibles to the vertebrae. Different parts of this layer, therefore, 

 serve to draw the mandibles together, to protract and retract the hyoid cartilage, and to 

 lower the under jaw. 



It is interesting to find a whole group of muscles represented only by a single unbroken 

 layer. This is perhaps an instance of arrested development or more properly reversion, 

 consequent upon the reduction of the shoulder girdle and the visceral skeleton. Vetter 

 (xiv) has shown that in the selachians, there is a constrictor superficialis, which in its 



