OF REPTILES AND BIRDS. 7 



muscles, which lie closely compacted in a continuous core. The sheath is composed of 

 connective fibres, running transversely but irregularly, crossing one another at slight 

 angles, and not united into bundles. From the common sheath arise fascia3 and 

 partitions of connective tissue, which extend around the single muscles, and in between 

 the fibres and bundles of fibres, of which they are composed. 



The muscular fibres are long, and their striation very distinct. In the preparation 

 now under examination, they show no tendency to unite in bundles, differing in this 

 respect not only from the other muscles of snakes, but also from the lingual muscles of 

 Ameiva, Chamaeleon, Mhnus, and mammals. In some sections through a retracted 

 tongue there appears a slight tendency to foi'm bundles of fibres. In transverse sections 

 it can be very plainly seen, that the sarcolemma is well developed, that the " Grund- 

 substanz" is pale and transparent, and that the darkly t^iamedJibriUulae are each entirely 

 distinct, and scattered irregularly, though always tending to unite in fibriUae, and some- 

 times plainly so united. The nuclei are about the same diameter as the Jlbrillae. They 

 occupy varying positions inside the fibre, but rarely lie in the centre, and never, so far as 

 I have observed, against the sarcolemma. 



The muscles of the tongue are five : — Longitudinal, 1, Ceratoglossi. 2, Lingualis. 

 Transverse. 3, Transversus superior. 4, Transversus inferior. 5, Verticalis. 



The ceratoglossi, c.gl, are inferior; the lingualis, I, superior, as is also the trans- 

 versus siqjerior, tr.s ; the verticalis, v, is median ; the transversus inferior, tr.i, is lat- 

 eral, but in the posterior part of the tongue, fig. 10, lateral and inferior. 



The muscular tissue is abundantly supplied with blood vessels, which run parallel to the 

 fibres, and are for the most part about half their diameter. The vessels have an elastic 

 fibrous tunica propria, and endothelial intima. In some places, where the larger arteries 

 have been cut through, the endothelium is shown in section with perfect distinctness, 

 fig. 13. The thin endothelium is quite pale, with few granules and pale oval nuclei, over 

 each of which the endothelium is thickened or bidging. The elastic coat is thick and 

 darkly stained ; it contains annular connective fibres, and small, round, darkly stained 

 nuclei. 



In figs. 7 and 8 there appears two pairs of nerves B and C I think B is probably the 

 lingual nerve ; C is the hypoglossus. B is accompanied by an artery, and considerable 

 loose connective tissue. C lies in the midst of the ceratoglossal muscle. Each nerve 

 is inclosed in a fibrous sheath, the neurilemma, and consists entirely of niediiUated fibres, 

 in sections of which the three comjDonent parts, axis-cylinder, medullary sheath, and 

 Schwann's sheath, all appear very plainly, fig. 4. 



The epithelium extends of course only over the free part of the tongue. Near the 

 point of attachment, the epithelium resembles that of the sheath of the tongue, being 

 distinctly divided into a mucous and hoi'ny layer, and is of nearly uniform thickness and 

 character upon all points of the section {cf. fig. 9). The horny layer extends with certain 

 exceptions over the whole of the tongue, but in no part of it is the cellular character of 

 the layer so much obscured, as is the case when the cornification is complete, as upon the 

 tongue of Mimus. In sections through the middle of the free part of the tongue, the 

 epithelium presents several characteristic peculiarities, fig. 8. The corneous layer 

 is interrupted at the furrows, F. The mucous layer is much thinner on the ventral than 



