10 MR. G. GULLIVER ON THE [Jan. 2, 



4. On the (Esophagus of the Pied Hornbill (Toccus melano- 

 leucus) : being an Appendix to a paper on the Taxo- 

 nomic Character of the Muscular Sheath of that Tube as 

 regards Sauropsida*. By George Gulliver, F.R.S. 



[Received December 2, 1871.] 



Through the courtesy of Mr.. Sclater I have had an opportunity 

 of examining the viscera of the Pied Hornbill (Toccus melanoleucus) 

 that died in the Society's Menagerie on the 23rd of November, 1871. 

 It was a male bird ; and the cause of its death was tubercular peri- 

 tonitis — that scourge of the Vertebrates in the Society's Gardens. 



In the memoir cited above it was shown that Birds and Reptiles 

 may, by the single character of the want of a sheath of transversely 

 striated muscular fibre on the oesophagus, be sharply defined from 

 Mammals and Fishes, in which last two classes more or less of the 

 length of the oesophageal sheath is, on the contrary, regularly com- 

 posed of muscular fibre that is transversely striated. 



But it remains for inquiry whether exceptions may not be found 

 to this rule. And these, were we to judge from function of struc- 

 ture, might be confidently expected in Birds ; for in this class we find 

 numberless instances of a voluntary and habitual regurgitation or 

 ejection of matters from the upper part of the alimentary canal. 

 And yet in none of these cases has the oesophagus or stomach been 

 found with an investment of that striated fibre which belongs to the 

 voluntary muscles of the skeleton of the species. If, therefore, either 

 of these parts of the alimentary canal be the active agent in such 

 regurgitation or ejection, the voluntary muscles of that part must be 

 of the smooth kind, as, indeed, they are well known to be through- 

 out the frame in several classes of Invertebrates. 



Among Mammals, the Ruminants have been proved to possess an 

 oesophageal sheath of striated muscle, as was expected in these 

 animals j and it has accordingly been described as if characteristic 

 of this order. Thus the Ruminants are the only Mammals in which 

 this kind of muscular fibre has been noticed by the author of the 

 'Comparative Anatomy of Vertebrates' as belonging to the oesopha- 

 geal sheath. " The oesophagus is frequently concerned in regurgi- 

 tation ; and in the Birds in which this phenomenon occurs the 

 muscular coat of the gullet, like that in Ruminants, is well deve- 

 loped" (vol. ii. p. 158). "In true or ordinary Ruminants the mus- 

 cular fibres of the oesophagus are disposed in two layers of spirals, 

 taking reverse directions, which decussate at one or other of two 

 opposite longitudinal lines; the outer layer contains more muscular 

 and less cellular tissue than the inner one ; the fibres of both are of 

 the striated kind ; and, as is usual when such are in more habitual 

 and energetic action, they are of a redder colour than in non-rumi- 

 nating Mammals" (vol. iii. p. 4/0). 



* See P. Z. S. 1870 ; p. 283. 



