240 REPORT — 1846. 



In mammals the normal completion of the hyoidean arch, as it first ap- 

 pears in fishes, is again resumed, and that not by a slender cartilage, as in 

 the frog, but by a chain of bones, in which we again recognise the cerato- 

 (fig. 24, 40), epi- (39) and stylo- (3s) hyals suspending the basihyal (41) and 

 the tongue to the base of the skull, often to the petrosal, sometimes to the 

 tympanic, or to the mastoid, or to the exoccipital. The ungulates and the 

 true carnivora best display this type. 



In man (fig. 25) the ceratohyals are reduced, as in birds, to mere tuber- 

 cles of bone (40), and the extent of the arch between them and the stylo- 

 hyals, which become anchylosed to the temporal bones, retains its primitive 

 ligamentous condition. Occasionally, however, ossification extends along 

 the stylohyoid ligament, and marks out, as in the specimen figured by 

 Geoffroy St. Hilaire (Philosophic Anatomique, pi. 4, fig. 87), the more nor- 

 mal proportions of the ceratohyal, and also the epihyal. Other examples of 

 this ' monstrosity' are recorded in works on anthropotomy. The thyro- 

 hyal (46) — the last remnant of the branchial arches — maintains more con- 

 stancy in its existence and proportions ; but manifests its true character of 

 free suspension below the skull, and an articulation by short ligaments to the 

 angles or horns of the thyroid cartilage. 



The remarks already made on the special homologies of the parts of the 

 scapular arch and its appendages, preclude the necessity of further extending 

 the present part of this Report. 



Part II. — General Homology. 



On taking a retrospect of the results of the researches of anatomists into 

 the special homologies of the cranial bones, the student of the science, how 

 little soever practised in such inquiries, cannot but be struck with the amount 

 of concordance in those results. It must surely appear a most remarkable 

 circumstance to one acquainted only with the osteology of the human frame, 

 that so many bones should be, by the common consent of comparative ana- 

 tomists, determinable in the skull of every animal down to the lowest osseous 

 fish. .This fact alone, so significant of the unity of plan pervading the ver- 

 tebrate structure, has afforded me, at least, a large ground of hope and 

 much encouragement to perseverance in the reconsideration of those points 

 on which a difference of opinion has prevailed ; and in the re-investigation of 

 what is truly constant and essential in characters determinative of special 

 homologies. 



In this, as in every other inquiry into nature, the first, labours are neces- 

 sarily more or less tentative and approximative : but if errors have to be 

 eliminated in the course of successive applications of fresh minds to the 

 task, truths become confirmed and established. And I regard the body of 

 such truths (see Table I.) to be now so great, in respect of the determination 

 of the homologous bones in the heads of all vertebrate animals, as to impe- 

 ratively press upon the thinking mind the consideration of the more general 

 condition upon which the existence of relations of special homology depends. 



Upon this jaoint the anatomical world is at present divided, lacking the 

 required demonstration. The majority of existing authors on comparative 

 anatomy have tacitly abandoned*, or with Cuvier and M. Agassiz, have 



* Wagner, ' Lehrbuch der Zootomie,' 8vo, 1843, 1844. Siebold and Stannius, ' Lehr- 

 buch der Vergleichende Anatomie,' 8vo, 1845, 1846. Milne-Edayards, ' Elemens de 

 Zoologie,' 8vo, 1834. Prof. Rymer Joxes, ' Outline of the Animal Kingdom and Manual 

 of Comparative Anatomy,' 8vo. 1841. The sentiments which this pleasing and instructive 

 writer expresses, are probably akin to those which have influenced the above-cited authors 



