1144 



TONGUE. 



sitions, constitute its possession, or any oral 

 process, to which no other name can be assigned, 

 is called a tongue. But when we enter the 

 Vertebrata we find an organ of characteristic 

 structure, conforming to a general type, pos- 

 sessing many common characters, of a form 

 whose varieties are not so great as to prevent 

 its being the name of a particular shape, and 

 always constituted of those three systems 

 previously enumerated as essential to the 

 tongue of Vertebrata. I shall first consider 

 the comparative anatomy of the bony system 

 of the tongue in all Vertebrata, and then briefly 

 refer to some of the principal characters of 

 the organ itself in the four classes into which 

 that subkingdom is divided. 



Hyoid apparatus. The comparative ana- 

 tomy of the hyoid apparatus is a subject of 

 high interest, as it enables us, by its reflected 

 light, to read successfully the true nature and 

 value of the different elements of the structure 

 as met with in man and other mammalia. It 

 shows us, with the certainty of a demonstra- 

 tion, and the contrariety almost of a paradox, 

 that the hyoid bone in man, which we are ac- 

 customed to look upon as a single bone whose 

 dismemberment depends merely on late ossi- 

 fication, is, in reality, a composite structure 

 a contribution from two distinct systems of 

 bones ; that while the body and lesser cormia 

 form part of the true endoskeleton, and are 

 congeneric with the bony framework of the 

 trunk and limbs, the greater cornua form part 

 of the visceral or splanchno- 'skeleton, and are 

 congeneric with the maxilliform supports of 

 the teeth of the stomach of the lobster, or the 

 bony pieces situated in the auriculo-ventricular 

 ring, in the hearts of ruminants, or with other 

 similar structures ; and that, as we must look 

 upon these in regard to the function they sub- 

 serve, as respectively digestive and circulatory 

 bones, so we must regard the greater cornua 

 of the hyoid as respiratory. 



To prove the truth of this proposition, it 

 will be necessary to examine the state of the 

 hyoid apparatus in water-breathing animals, 

 and to connect its condition as found in these 

 with what we find it in air-breathers, by tra- 

 cing the modifications which its different parts 

 undergo in those animals, part of whose ex- 

 istence is destined to the respiration of water, 

 and part to that of air ; we shall thus gain a 

 clear insight into their homologies, and be 

 able to refer part to part without the chance 

 of fallacy, inasmuch as the link of their con- 

 nection is lodged not in different individuals, 

 but in different parts of the life of one. I 

 shall describe it, 



1st., in fish. Professor Owen has shown 

 that the different segments of the true hyoid 

 arch are so many elements of the inverted or 

 haemal arch of the third cranial vertebra. 

 The centre of this arch in fishes (fig. 760. A) 

 is formed by four small, subcubical bones, the 

 basi-hyals (b '//) (two only are represented in 

 the figure, being seen in profile), from the 

 sides of which extend upwards, backwards, 

 and outwards, two long and stout cylindrical 

 pieces, the cerato-hyals (c /i) ; the summit of 



each of these is surmounted by a small trian- 

 gular piece, the epi-hyal (ep h), and the arch 

 thus constituted is suspended on each side, to 

 the base of the skull, by a small, slender 

 ossicle, the stylo-hyal (st A), which may be 

 considered either as the entire proximal piece 

 of the hyoid arch, or a dismemberment of that 

 piece, according as the posterior division of 

 the epitympanic, to which it is attached, 

 is looked upon as the displaced proximal 

 piece of the next arch in advance, the tym- 

 pano-mandibular, or as itself the proximal 

 element of the hyoid. This completes the 

 hyoid arch : in most fishes, however, there are 

 two more bones attached to the centre of the 

 apparatus, one stiliform, projecting forwards, 

 appended to the anterior surface of the median 

 symphysis of the basi-hyals, the glosso-hyal 

 (g h), the true lingual or tongue-bone; the 

 other, the uro-hyal(u h), a vertically-expanded, 

 triangular piece, extending backwards from 

 the posterior surface of the basi-hyals. There 

 are generally appended to the posterior and 

 lateral surface of the cerato-hyals and epihyals 

 a series of slender, slightly curved rays, 

 varying in number from three to thirty, but 

 generally about seven, as in the cod (Gadus 

 Morrhua) (fig. 760. A) ; their office is to sup- 

 port the membrane that covers in the branchial 

 chamber, whence they are called branchio- 

 stegals (b,b). 



Immediately behind the hyoidean arch, we 

 meet with a system of arches, the branchial, 

 whose office is to support the gills, and whose 

 structure, position, development, and con- 

 nections prove them to have no relation with 

 the true skeleton : they are generally five in 

 number; the four anterior being branchial, the 

 last, which is dentigerous and guards the 

 gullet, pharyngeal. Each arch rises laterally 

 from a median chain of ossicles attached to 

 the basi-hyal, or uro-hyal when ossified, and 

 consists of a short inferior piece, the hypo- 

 branchial, surmounted by a long, curved piece, 

 the cerato-branchial, bending first outwards 

 and upwards, then forwards and inwards, 

 under the base of the cranium. Now, these 

 arches are what were just now stated to be 

 homologous with the posterior or greater 

 cornua of the hyoid apparatus, in all vertebrate 

 forms, whenever they exist ; that they are so, 

 will best be shown by tracing the modifica- 

 tions they undergo in the metamorphoses of 

 the anourous batrachians. Fig. 760. B, 1. re- 

 presents the hyoid and branchial apparatus in 

 the water-breathing tadpole ; B, 2, where the 

 same animal has become the air-breathing 

 frog. In the full-gilled tadpole (B, 1), a simple 

 basi-hyal (b h) supports laterally two cerato- 

 hyals (c h}, and posteriorly two short hypo- 

 branchials (h b), to each of which are attached 

 four cerato-branchials (c b). The second stage 

 is marked by the divergence and growth of the 

 extremities of the hypo-branchials and the pro- 

 gressive absorption of the cerato-branchials. 

 At the third stage, the cerato-branchials have 

 disappeared, and the hypo-branchials have 

 assumed the character of true greater hyoidean 

 cornua (B, 2, h b). In the fourth stage they 



