940 



TEMPORO-MAXILLARY ARTICULATION. 



manner of trace to indicate where the joint 

 once was. In fact this anchylosis had existed 

 for fifty years before the death of the patient. 

 No record is preserved of the cause of it. 

 The joint of one side only is anchylosed, but 

 that of the other side is much altered in form. 

 An abnormal tubercle of bone projects down- 

 wards from the middle of the glenoid cavity 

 and is received into an abnormal excavation 

 or alveolus in the middle of the condyle. The 

 lower jaw is much wasted in size, and has lost 

 all its teeth save the two front incisors. The 

 upper jaw bones are thin and light. 



The motion of the lower jaw is often lost 

 owing to an affection not immediately con- 

 nected with the joint itself. When, as often 

 happens in scarlatina, cancrum oris, &c. there 

 is extensive sloughing of the inside of the 

 cheeks, the cicatrices resulting from the heal- 

 ing of the great wounds contract, and form 

 bands, extending from the upper to the lower 

 jaw, so strong and unyielding that the muscles 

 which open the mouth are unable to antago- 

 nise them. 



COMPARATIVE ANATOMY. If a palaeonto- 

 logist were asked what fragment of a verte- 

 brate skeleton, speaking generally for all ver- 

 tebrata, would give him most information as 

 to the status and affinities of the animal to 

 which it belonged, he would most probably 

 answer the articular portion of the lower 

 jaw or the articulation that receives it. Of 

 the convex and concave surfaces which go to 

 form this articulation, in all the mammalia 

 the convexity is on the inferior maxilla, and 

 the concavity on the squamosal bone, whilst 

 in the three other vertebrate classes the re- 

 verse is invariably the case the concavity is 

 on the inferior maxilla, the convexity on the 

 bone that articulates with it. 



The under jaw does not articulate with the 

 same, or to speak more accurately, with the 

 homologous bone in all vertebrate animals. 

 In all the mammalia it articulates, as in man, 

 with the squamous element of the temporal 

 the squamosal bone. In birds, reptiles, and 

 osseous fishes it articulates with bones which 

 are clearly the special homologues of the tym- 

 panic ring of the human subject. In cartila- 

 ginous fishes its articulation is with the pter}'- 

 goid bone, the hotnologue of the human 

 internal pterygoid plate. The Lepidosiren, 

 in which so many other characters of the 

 osseous and cartilaginous fishes are so curi- 

 ously blended together, in strict accord with 

 this circumstance, presents an instance of the 

 pterygoid and tympanic bones contributing 

 each a part the former the inner, the latter 

 the outer part, of the articular surface for the 

 reception of the lower jaw.* 



It is well worth while to stop here and 

 review what is stated in the two preceding 

 paragraphs. What is said is, really, this ; 

 every animal that suckles its young has a convex 

 articular surface to its lower jaw, whilst every 

 vertebrate that lays eggs has a concave sur- 

 face. Or this every vertebrate animal that 



has hair upon it, that has a diaphragm, or an 

 epiglottis, has a convex articular surface to 

 its lower maxilla, whilst all vertebrates that 

 are destitute of these have a concave surface. 

 Or, again, all animals that suckle their young, 

 and have diaphragms, hair, and epiglottides, 

 present their squamosal bones for the articu- 

 lation of their inferior maxillae, whilst all in 

 which the possession of these characters is 

 negatived present for this articulation their 

 tympanic, or, rarely, their pterygoid bones. 

 Can any physiological reason be assigned for 

 this ? Can any final purpose, holding good in 

 all, or in the majority of, instances, be shown 

 to be served by this difference ? I think none 

 can. One cannot conceive but that it is a 

 matter of perfect indifference whether the 

 convexity is on this bone or that. Let us look 

 once more to the facts. The bat that flies, 

 but not the swallow, the whale that swims 

 but not the cod-fish, the camel that walks the 

 desert, but not the ostrich, the carnivorous 

 lion, seal, and weasel, but not the eagle, 

 penguin, crocodile, and shark, have convex 

 articulations to their lower jaw and present 

 to them their squamosal bones. Here then 

 is a caveat for the physiologist. A character 

 found in an animal may have no physiological 

 signification, no relation to external circum- 

 stances, nor even a functional connexion with, 

 or dependence on other characters wherewith 

 it coexists, perhaps invariably. It may be due 

 to the status only of the animal. Physiolo- 

 gically independent it may exist in an animal 

 only because other independent characters 

 co-exist. It may be a Syneilogy, not a Teleo- 



logy- 



That certain independent characters in- 

 variably go together, which was so elaborately 

 illustrated by Cuvier, is a fact of a high order, 

 perhaps the twilight of some great truth. If 

 future investigations should prove that truth 

 to be progressive developement, towards which 

 hypothesis the inquirer is, even now, tempted 

 by so many striking facts, as well as by the 

 admirable use that can be made of it as a 

 scaffold theory, then we should say, and as 

 making use of a scaffolding we may say it now, 

 that certain characters are attained to at a cer- 

 tain stage in the chain of development, and, 

 therefore, those are found coexisting which are 

 proper to the degree of development to which 

 the animal has arrived. Such characters I 

 have been accustomed to call Syneilogies *, a 

 word which at all events has the merit of re- 

 ferring only to a well known fact, without in- 

 volving any hypothesis. To the palaeontologist 

 this " correlation of independent characters " f 

 is, of course, invaluable, and for the purpose of 

 arranging wa^wra/ groups in the animal kingdom, 

 these, so to speak, useless, or Syneilogical, cha- 

 racters are immeasurably more valuable than 

 those modifications to meet special exigencies 

 which are called teleologies. 



Mammalia. In all mammalia, except man, 

 the articular surface on the squamosal bone is 

 bounded posteriorly, or, in the rodents, inter- 



Owen. 



f Cuvier. 



