248 



NATURE 



[Jan. 25, 1872 



compared by Cuvier to the tympanic bone of mammals, 

 but which more lately, in consequence of the embryo- 

 logical researches of Reichert and Rathke, was held to 

 correspond rather with the incus, — a view in which Prof. 

 Huxley formerly concurred. Later observations, however, 

 (detailed in a paper published in the Proceedings of the 

 Zoological Society for 1869) have led him to alter his 

 opinion, and to form the opinion that the os quadratiiiii 

 may, with the greatest probability, be regarded as repre- 

 senting the malleus. 



In explaining this morphological point. Prof. Huxley 

 refers as fuUows (at p. 27) to the osteogenetic process 

 connected with the formation of the lower jaw andhyoid 

 bone, or mandibular and hyoid arches. 



"Two ossifications commonly appear near the proximal 

 end of Meckel's cartilage, and become bones moveably 

 articulated together. The proximal of these is the quad- 

 rate bone found m most vertebrates, the malleus of 

 mammals ; the distal is the os articulare of the lower 

 jaw in most vertebrates, but does not seem to be repre- 

 sented in mammals. The remainder of Meckel's carti- 



lage usually persists for a longer or shorter time, but does 

 not ossify. It becomes surrounded by bone, arising from 

 one or several centres in the adjacent membrane, and the 

 ramus of the mandible thus formed articulates with the 

 squamosal bone in mammals, but in other vertebrata is 

 immoveably united with the os articulare. 



" Hence the complete ramus of the mandible articulates 

 direcdy with the skull in mammals, but only indirectly, or 

 through the intermediation of the quadrate, in other ver- 

 tebrata. In birds and reptiles, the proximal end of the 

 quadrate bone articulates directly (with a merely apparent 

 exception in Ophidia), and independently of the hyoidean 

 apparatus, with the periotic capsule. In most if not all 

 fishes, the connection of the mandibular arch with the 

 skull IS effected indirectly, by its attachment to a single 

 cartilage or bone, the liyomaiidibular, which represents 

 the proximal end of the hyoidean arch." 



This last " is often united, more or less closely, with the 

 outer extremity of the bone, called columella amis, or 

 stapes, the inner end of which, in the higher vertebrata, 

 is attached to the membrane of the fenestra ovalis." 



Fig, 7.— The Skeleton of 



A fuller and most interesting account of the origin and 

 relations of these boies in connection with the changes 

 occurring in the development of the first and second 

 visceral arches, and with the formation of the external 

 and middle parts of the ear is given at pp. 83— S5 ; but 

 there is only space here to reproduce the diagrammatic 

 figure of the IManual (Fig. 2), which places very clearly in 

 comparison their probable homology in fishes, reptiles, 

 and mammals. 



The main point on which the question hinges seems to 

 be the separate connection ascertained to exist between 

 the periotic capsule and the two rods contained respec- 

 tively in the first and second visceral arches ; the proxi- 

 mate part of the first becoming the quadrate bone, or 

 malleus; that of the second becoming the incus in the 

 part above the attachment of the stapes to the rod, and 

 stapedius muscle below ; while the stapes itself, or 

 columella auris, is an offset, as it were, from the second 

 rod proceeding to the fenestra ovalis. The subject, how- 

 ever, is one O' so great diffii ulty, especially as connected 

 with the existence and relations of the tympanic bone in 

 birds and reptiles, to the proof of which the researches of 

 Peters have been directed, that it would be hazardous 

 to attempt any decision of the question at issue without 



an opportunity of going very fully and minutely into the 

 whole investigation. 



The third iUustration from the earlier part of the Manual 

 (Figs. 3, 4) gives a clear view of the relations now very 

 generally recognised between the rudimentary parts of 

 the fcetal brain and those forming the adult encephalon 

 of the different classes of Vertebrata ; and it is enough to 

 refer to the diagrammatic figures, with their description. 



The exposition which follows of the modifications in the 

 form and organisation of the brain in different animals, to- 

 gether with the comparative views of the brains of the rab- 

 bit, pig, and chimpanzee, in figs. 21 and 22 of the Manual, 

 is most instructive and worthy of attentive study. 



The next illustration extracted from the Manual (Fig. 5) 

 is diagrammatic, like the preceding ones, being intended to 

 explain the changes by which, in fishes and amphibia, the 

 permanent arterial vessels nearest the heart are derived 

 Irom the common typical aortic arches, which, in the 

 fcetus of all vertebrate animals, surround the first part of 

 the alimentary canaL 



The illustration might advantageously be extended to 

 show the parallel changes in reptiles, bird?, and mammals; 

 these, however, may be better given from the ventral than 

 from the lateral aspect. 



