March 22, 1888] 



NATURE 



501 



censed to possess the aptitude as a whole for receiving all kinds 

 of impressions from without, and in fact it is this general apti- 

 tude that has rendered possible the evolution of the special 

 senses in special centres. Thus the common origin of all the 

 senses would seem to offer the readiest explanation of their 

 occasional confusion even in the human brain itself, the highest 

 development of all. Colour-hearing might in this way be 

 regarded somewhat as a case of reversion or atavism. 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, February 23. — " On Remnants or Vestiges 

 of Amphibian and Reptilian Structures found in the Skulls of 

 Birds." By W. K. Parker, F.R.S. 



(i) Jacobson's Organ. — This remarkable structure, which must 

 be looked upon as an accessory olfactory organ, is present in 

 certain of the higher Vertebrata, or Amniota. It consists of a 

 paired cavity, which early becomes separated off from the proper 

 nasal chamber, and which opens into the mouth by the anterior 

 incisive foramen. It is innervated by branches from the olfactory 

 and trigeminal. 



Jacobson's organs are largest in Snakes, Lizards, and Mono- 

 tremes, and next in order come the Marsupials, Edentates, 

 Insectivores, and the Mammalia genei'ally. Their presence in 

 Man is doubtful, and what has been described as a rudiment of 

 them ha-; probably quite another explanation.^ They are not 

 known to exist in Chelonians, Crocodiles, and Birds. 



In the Snake and Lizard, these structures lie each in a little 

 dish, formed by the vomer of that side, covered in by another 

 vomerine bone — the septomaxillary. They are also protected at 

 the opening of the capsule by a pedate tract of cartilage, derived 

 from the alinasal fold, which, in the Snake, frequently becomes 

 detached from its root. In low Mammalia there are several 

 vomers, and in most of the lower Mammals a pair of small 

 anterior vomers lie on the inside of Jacobson's organ, but the 

 capsule itself is formed by a peculiar fold of cartilage — the re- 

 current cartilage, — which closes in upon itself, and unites its 

 edges round the organ. As a rule, these "recurrent cartilages " 

 retain their union with the alinasal folds, as in the Lizard ; in 

 the Rabbit (Howes) they are distinct, as in the Serpent. 



Now in Birds these cartilages not unfrequently appear, but no 

 Jacobson's organ has been found with them. The Birds whose 

 vomerine region comes nearest to that of a low Mammal are the 

 Turnicidffi, or Hemipods, and t'le great group of the Passerine 

 birds (Coracomorpha;, or .i^githognathee of Huxley). It is not 

 uncommon for the "ox-faced " vomer of these birds to be formed 

 of two pairs of bony centres, and these become not only fused 

 together, but actually grafted upon the floor of the cartilaginous 

 nasal capsule, in the same' manner as is common in the lower 

 kinds of Mammalia. 



Remnants of the cartilaginous capsule of Jacobson's organ> 

 are found not only in the Hemipods and in the lower Neotropical 

 Passerines {Ho/nonis, Syiiallaxis, Aticercfes), but also in some of 

 the highest of the singing-birds — namely, the Wren {Anorthitra 

 tn\i;;/odj'/cs) — and also in some of the Woodpeckers (Picida;), out- 

 side the Passerine Order. 



In a paper on the "Skull in the Ostrich Tribe" (Phil, Trans., 

 1886, pi. 10, Fig. 14, a.i.L), the present author figured and de- 

 scribed, but did not then fully understand, a peculiar cartilage 

 perched right and left upon the large vomer of the K/ica, He, 

 however, has for a long time been satisfied that this is one of the 

 vomerine or Jacobson's cartilages, and this view is strongly 

 corroborated by the recent description of the palate of Aptcryx, 

 given by T. Jeffery Parker (Proc. Roy. Soc, February 23, 1888), 

 Now if the figure of the transversely-vertical section through 

 these cartilages and the crura of the vomer in the Aptcryx, be 

 comparted with various figures in the present author's " Memoirs 

 on the Mammalian Skull" (Parts L, II., and HI., "Phil. 

 Tran<.''), it will be seen that it so nearly corresponds with 

 sections of the skull of the Pig, the Edentates, and the In- 

 ' scctivores, especially those taken just behind Jacobson's organ. 



See Gegenljaur, " Ueber'das Rudiment einer septalen Nasendruse be!m 

 Mciischen,' Morplwl. Jahrbuch, Bd. xi., 1885. At the time when the pre- 

 sent p.iper was read, the author was net aware of Gegenbaur's conclusions 

 with regard to the supposed rudiment of Jacobson's organ in Man. 



that without explanation it would be impossible to tell which 

 figure belonged to the Bird, and which to the Mammal. 



(2) Parasphenoid. — This bone forms a large superficial basi- 

 cranial beam in Ganoidei, Teleostei, Dipnoi, and Amphibia. 

 It corresponds to the subcutaneous part of a dermal scute formed 

 inside the skin of the mouth, developed for support to badly 

 ossified endocranium. 



The parasphenoid of the Frog is dagger-shaped, and reaches 

 from near the foramen magnum behind, to the nasal capsule in 

 front, the "guard" of the dagger supporting the auditory 

 capsules. Now in Serpents only the blade is present ; in Lizards 

 only a very fine thread of bone representing the blade ; in some, 

 e.g. Trachydosatiriis riigostis (Cyclodonlidas), even this is 

 wanting. It is not present in those very amphibian forms, the 

 Chelonians ; and only a small remnant of the "guard " right and 

 left can be found in Crocodiles, consisting of two " basitemporal " 

 plates, soon covered over by the huge pterygoid. 



In all Birds basitemporals are large, as large as in Frogs and 

 Toads ;_ this is equally true of the Dinornis and of the smallest 

 Humming-bird, There is a tendency for them to break up into 

 lesser bony parts ; thus for a day or two in the chick there are 

 two " basitemporal " and one "rostral" centre; but in several 

 species of the Ranidae, e.g. the Bull-frog, the point of the 

 dagger-shaped bone is separately ossified, and remains distinct. 



In the Paradoxical Frog {Psettdis paradoxa) there is no 

 "handle" to the dagger; the same form of parasphenoid is 

 common among the water-birds, e.g. Aha, Uria. This is an 

 ossification which is the earliest to appear in skulls that take on 

 any kind of ossification ; it is also the first bone to appear in an 

 embryo bird, as in the larval Frog. 



(3) Prenasal Kostnim. — Scarcely any Urodeles, and only a few of 

 the Anura, show any special elongation of the "intertrabecula " or 

 prenasal rostral cartilage ; this must have been very long in the 

 Ichthyosauria, as in the Selachii, and as in the embryos of all 

 Birds. 



(4) Palatopterygoid arch or arcade. — In the Frog, after meta- 

 morphosis, during which the hinge of the jaw becomes shifted 

 far backwards, three regions may be distinguished in the fore- 

 part of this arch ; thus the suspensorial part or pedicle is the 

 ethmo-palatine, the anterior free spike the pre-palatine, and 

 the hinder part which runs into the pterygoid is the post- 

 palatine. 



The anterior part of the pterygo-palatine arcade is distinct from 

 the pterygoid in Urodeles, and the pterygoid in them is an out- 

 growth of the quadrate which grows forwards towards the 

 palatine, but does not coalesce with it, except in Ranodon 

 sibiricus.^ The "post-palatine" tract of cartilage is developed 

 as a distinct nucleus in the Axolotl (Sircdon).'^ 



The only Reptiles in which the author has discovered any 

 distinct trace of the endoskeletal palatine is in the Green Turtle, 

 in which it is very small (see Challenger Reports, vol, i. part 5, 

 plate 12, Figs. 9, 9a, 9/' : e.p.a.). 



This endoskeletal cartilaginous palatine, with Its peduncle and 

 fore and hind ray or crus, appears in several kinds of birds, in 

 addition to their normal parosteal palatine — a mere membrane 

 bone, as in Reptiles and Mammals, This vestige or remnant 

 remains in the adult ; it is of no apparent u e, and occurs in the 

 Families in the oddest way ; sometimes, however, it is present in 

 all the members of some particular Family-group, as for instance in 

 the Musophagida; or plantain-eaters {Miisophaga, Schizorhis, and 

 Corythaix).^ It is also found in the Oil Bird {Stcatornis cari- 

 pensis) and in the Green Tody ( Todiis viridis), and it is also well 

 developed in Scythrops (see Linn. Soc. Trans., ser. 2 (Zool.), 

 vol. i. plate 23, Figs. 3 and 4, o.n.). 



In that nearly extinct Neotropical type, Stcatornis, this curious 

 partly ossified remnant has the three crura, all well marked, and 

 their morphological meaning is evident ; albeit the whole piece is 

 so small and feeble that it can serve no purpose in the solid 

 palate of that remarkable bird. 



To show how unexpectedly this remnant exists, a list of the 

 Birds in which it has been found in a segmented state as a 

 distinct bony element of the face is added below ; it often shows 

 itself as a mere process of the ecto-ethmoid, but these cases are 

 not included in the list, 



' See Wiedershelm, " Kopfskelet der Urodelen," Leipzig, 1877, Plate 5, 

 Figs. 69, 70. 



» See W. K. Parker, "On the Skull of the Urodeles' (Phil. Tr.ins., 1877, 

 Plate 24, Figs. 1-3). 



3 See Reinhardt, " Om en hidtil ukjendt Knogle i Hovedskallen hos 

 Turakoerne (i'/?«o//;<7f/Vff, Sundev)," Copenhagen, 1871, Plate 7. 



