88 report — 1865. 



the fish — at any rate, that very strong reasons ought to be given before we are 

 called upon to renounce that which, upon the face of it, is so probable. 



The squamous part of the temporal bone to which the lower jaw is, directly or 

 indirectly, invariably attached, is in mammals always composed of one bone, and 

 developed from one centre, like the lower jaw ; and like it, it consists of certain 

 well-marked parts — a glenoid part, a squamous part, and a zygomatic part. 

 Dr. Humphry believes that as in the lower jaw the component parts of the mam- 

 malian bone correspond with the several bones of the ovipara, so, in the temporal 

 bone, the component parts of the mammalian squamous correspond with the 

 separate bones of this region in ovipara ; that is to say, the " glenoid " corresponds 

 with, oris homologous with, the "quadrate," the "zygomatic" with the " qua- 

 drato-jugal," and the "squamous" proper with the " squamosal." 



By Cuvier, and most subsequent anatomists, including Owen, the quadrate has 

 been regarded as the representative of the tympanic. In controverting this view, 

 Dr. Humphry showed that neither in position, in function, nor in development, 

 does the quadrate correspond with the tympanic. The tympanic bone is simply a 

 part of the auditory organ, having no relation whatever with the masticatory 

 apparatus. In the descending series of animals we find that the auditory organ 

 becomes simplified, part after part disappearing, till, in the fish, a membranous 

 labyrinth alone remains. And it is far more probable that the tympanic bone 

 shares this failure, and dwindles or disappears, than that it becomes magnified and 

 subservient to a totally different purpose. "We are, moreover, prepared for its 

 disappearance in the inferior classes by the very great varieties which it undergoes 

 in mammals, which were pointed out in considerable detail. It was shown, as the 

 result of dissection, that the quadrate does not commonly sustain the tympanic 

 membrane, and that in many reptiles this function is performed by a distinct ring 

 of bone resembling the tympanic bone of the mammalian foetus ; and this ring, 

 and not the quadrate, is really the representative of the tympanic bone. 



Dr. Humphry next proceeded to examine the view propounded by Vogt, and 

 adopted by Huxley, that certain of the ossicula auditus — the malleus and incus — ■ 

 are, in ovipara, modified and magnified so as to form part of the mandibular 

 pedicle, in short, that the malleus becomes the articular segment of the jaw, and 

 the incus becomes the quadrate. Such a transposition of parts, topographical as 

 well as functional, as is implied by this view is not, the author believes, in accord- 

 ance with the laws of development and morphology. Each organ, he observed, 

 throughout the animal world, is made to bear its own burden, and by the develop- 

 mental forces of its own parts furnishes the structures necessary to fulfil the re- 

 quirements made of it in the different members of the animal series. The com- 

 ponents of the eye are not transformed to the accommodation of the ear ; neither 

 can we think that the bones of the ear are transformed to the accommodation of 

 the mouth. 



The arguments in favour of the view referred to are founded chiefly upon deve- 

 lopment and the relations of the parts concerned to Meckel's cartilage ; and Profes- 

 sor Huxley has laid much stress upon these relations in the pike. But Dr. Hum- 

 phry maintained that, even in the pike, the articular bone of the jaw is, like the 

 dentary bone, developed, not in and around Meckel's cartilage, but on its outer side, 

 and is easily stripped off from it. Any homological inferences, therefore, deduciblo 

 from this relation apply to the dentary bone as strongly as to the articular bone. 



Dr. Humphry further showed, by the same kind of reasoning as in the case of 

 the tympanic bone, that the varying conditions of the auditory ossicles in mammals, 

 the coalescence of the malleus with the tympanic in certain cetaceans and in mo- 

 notremes, together with the small size or absence of the incus in the latter animals, 

 prepare us for the disappearance of those bones in the simpler auditory organ of 

 ovipara. He combated the idea that the development of the quadrate in cartilage 

 is any sufficient reason for regarding it as the representative of the incus, believing 

 that the mode of development of a bone in cartilage, or from membrane, is not to 

 be laid much stress upon as a matter of homological significance. 



The careful consideration of the matter from a development, as well as from a 

 topographical and functional point of view, convinced him that we must not suppose 

 either the tympanic bone or any of the auditory ossicles to be represented by the 



