NA TURE 



[Dec. 25, 1873 



larval Archegosaunis) has a similar pair of occipital con- 

 dyles. The'interesting matter is that man and all beasts 

 have also two occipital condyles. Is this then a mark of 

 affinity, and can we, as it were, reach beasts by a short 

 cut through Batrachians, leaving all the reptiles and birds 

 on one side, as a special outstanding and diverging 

 development ? 



We shall presently see that other yet more striking 

 facts may be brought forward in support of the latter 

 view. Nevertheless it must be remembered that there 

 are fishes, thongh very few and exceptional, which also 

 possess a pair of occipital condyles, and that in one 

 respect most fishes are more like mammals than are any 

 Batrachians since they, like mammals, have a well ossified 

 median bone at the base of the skull in the occipital 

 region, a structure which all Batrachians, without a single 

 exception, are destitute of 



The second point of interest concerns the lower part, or 

 base, of the skull, which exhibits a striking agreement with 

 the same part as developed in bony fishes. 



This agreement consists in the fact that the middle of 

 the floor of the skull is not formed as in all beasts, birds, 

 and reptiles, by a deposition of bony substance in pre- 

 existing gristle (ossification of cartilage), to which name 

 Basi-sphcnoid is applied, but, as in bony fishes, by a great 

 bone called Parasp/wiwid, which shoots forwards and also 

 extends backwards to the hinder end of the skull floor, 

 but is formed by the deposition of bony substance in pre- 

 existing membrane. (Fig. 38, /(?;•.) 



Although this great membrane bone is constant in 

 Batrachians and bony fishes, and is represented, if at all, 

 only by minute rudiments in higher vertebrates ; never- 

 theless in serpents we once more meet with a far-reaching 

 and well-developed parasphenoid. 



Yet it can hardlv be conceived that serpents have car- 

 ried off from Piscine ancestors and carefully preserved 

 this peculiarity of structure which all their other class 

 fellows have lost. It seems much more probable that 

 this structure has independently appeared through the 

 action of peculiar conditions, and hence that we have 

 here again a remarkable instance of the independent 

 origin of similar structures. 



The third peculiarity of the frog's skull consists in the 

 form and conditions of the bony supports of the tongue. 



It would not be easy to find a better example of the 

 need of widely extended observations in order duly to 

 understand structures apparently very simple indeed. 



The bone of the tongue in man — the os hyoldes* — is a 

 small structure, and one to all appearance of little signifi- 

 cance. It is placed at the root of the tongue and above 

 the larynx, and consists of a body with a pair of processes 

 on each side, one large (the posterior or great cornu), and 

 one small (the anterior or lesser cornu, or corniculum). 



Even in man's own class (mammalia) the relative deve- 

 lopment of the parts may vary greatly. Thus the corni- 

 cula may be large and may each be represented by two or 

 three distinct applications as in the dog and horse. 



The cornua also may take on a development very much 

 greater than that existmg in man as is the case in some 

 other Mammals. These facts may prepare us to expect 

 much greater divergences in lower forms ; and yet through- 

 out the two great classes of birds and reptiles (as well as 

 beasts) — though varying conditions as to the proportions 

 of the parts present themselves— the os hyoides continues 

 essentially the same in structure, and even in the adult 

 frog this bone exhibits nothing but a rather wide " body " 

 with two long and slender " cornicula " and a pair of 

 shorter " cornua." 



Let us now pass for a moment to the other end of the 

 vertebrate sufj-kingdom. We find in fishes a complex 

 framework for the support of the gills, or structures, by 

 which they effect then- aquatic respiration. This frame- 

 work consists of a number of arches (placed in series one 



* So named from its rescmbUince to the Greek letter y. 



behind another) extending on each side of the throat up- 

 wards towards the backbone, and supporting on their 

 outer sides the gills or branchia, en which account they 

 are caUed the branchial arcJus. In front of these arches 

 and forming as it were the first of the series, is an arch 

 which ascends and becomes connected with the skull. 



Turning now to those Batrachians which breathe 

 throughout their lives in the manner of fishes, we find a 

 corresponding system of branchial arches. Thus in the 

 Siren we find a series of gill-supporting branchial arches, 

 placed behind another arch which is connected with the 

 skull. 



But the frog passes the first part of its life in a fish-like 

 manner, and in the tadpole accordingly we find an appa- 

 ratus similar to that of the Siren. There are, in fact, on 

 each side of the throat, four branchial arches, placed 

 behind another arch, which is connected with the skull. 

 As development proceeds these brancJiial Arches become 

 gradually absorbed and all but disappear. Relics of 

 them, however, exist even in the adult condition, and thus 

 serve to indicate the trtie nature of parts which otherwise 

 would be little understood. 



The central portion of the structure — that from which 

 arches diverge on each side — increases in relative as well 

 as absolute size, and becomes the "body" of the os 

 hyoides. That arch on each side which is connected with 

 the skull and is placed immediately in front of the 

 branchial arches, continues to be so connected and be- 

 comes one of the two "cornicula," while the rudimentary 

 relics of the branchial arches which persist become what 

 we have seen in the adult as the cornua of the os hyoides. 

 Thus the anatomy of the tongue-bone of the frog, 

 studied in its progressive changes, reveals to us that other- 

 wise unsuspected relations exist in certain parts of the 

 tongue-bone of man. It exhibits to us the coruna of his 

 OS Iiyoidcs as related to those large and complex branchial 

 arches which play so important a part in the fish and form 

 so relatively large a portion of its skeleton. 



The fourth circumstance (the last here to be noticed) 

 connected with the frog's skull concerns the relative posi- 

 tion and size of certain of its enveloping bones. 



When the skull of the frog is viewed from above, a 

 large vacuity is seen to exist on each side, between the 

 brain-case and the great arch of the upper jaw. In the 

 hinder part of this space is situate the temporal muscle, 

 which by its contraction pulls up the lower jaw and closes 

 the mouth ; and the hollow in which this muscle lies is 

 called the temporal fossa. 



In a certain frog before noticed, called Ptloiaies, as also 

 in Calyptoccphalus, a similar view of the skull exhibits no 

 such great vacuity. The reason of such absence is that the 

 temporal fossa in these animals is roofed over and en- 

 closed by the meeting together of bony lameUffi developed 

 from the bones surrounding it, which thus bound the 

 orbit posteriorly, and give to the cranium an altogether 

 false appearance of great capacity. 



This very singular structure is found to exist also in the 

 marine turtles, amongst the Chelonians, and here we have 

 another striking resemblance between the Chelonia and 

 the Anoura, apparently reinforcing the argument for the 

 existence of real affinity derived from the presence of such 

 bony dorsal shields in both those two orders. The im- 

 portance of this character might seem the more unques- 

 tionable, since no other reptiles and no birds or beasts 

 whatever were known to exhibit a similar structure. 



Quite recently, however. Prof Alphonse Milne- Ed\yards 

 has described a beast from Africa [Lophioinys) belonging 

 to the Rodent (rat, rabbit, and squirrel) order, which has 

 a skull, the temporal fossa of which is similarly enclosed 

 by bony plates. 



This unexpected discovery completely destroys any 

 weight which might be attached to this character as an 

 evidence of genetic affinity. It does so because it is in- 

 conceivable this Rodent should have directly descended 



