Experimental studies on the columella-capsular interrelationship in the turtle Chelydra serpentina

The reciprocal effect of two neighbouring structures of different origins on each other during development is of considerable interest to the embryologist. Such a relationship exists between the columella auris and the auditory capsule in the vicinity of the fenestra ovalis. This particular relationship, in addition, embraces an aspect of fundamental importance to the morphologist viz. the possible derivation of part of the columella from the capsule. The vast literature pertaining to this latter aspect and particularly in regard to the development of the human stapes, was recently reviewed in great detail by Strickland, Hanson & Anson (1962). References to literature related to other vertebrates are found in e.g. van der Klaauw (1924), Versluys (1936), and Werner (1960). An earlier paper (Toerien, 1963) deals with the rather specialized problem of Amphibian stapes development The results of certain extirpation procsduivS on early embryos of the turtle {Chelydra serpentina) throw interesting high on the columella-capsule interrelationship.

Experimental Studies on the Origin of the Cartilage of the Auditory Capsule and Columella in Ambystoma

On the basis of earlier experimental results on amphibia and his own observations, Yntema (1955) came to the conclusion that the ‘ear rudiment or the ectoderm surrounding it may be a source of mesectoderm for the ear capsule, at least in the heterotopic position’. This is contrary to another view that the source of the cartilaginous ear capsule is of purely mesentodermal origin. The literature pertaining to these two points of view is reviewed by Yntema (1955) and Benoit (1957). The purpose of the present investigation is to study further the extent of the ectomesenchymal contribution to the auditory capsule in the orthotopic position. Ambystoma punctatum larvae were raised from eggs sent to this institute by Mr Glenn Gentry of Donelson, Tennessee. Some of the eggs were stained with Nile blue sulphate according to the method described by Detwiler (1917).

On the Head of the Liopelmid Frog, Ascaphus Truei

This paper gives the first account of the larval cranial anatomy of either of the genera of Liopelmid frogs. A single, partly grown larva of Ascaphus truei, Stejneger, has been studied in transverse sections and in two-dimensional reconstructions. Its chondrocranium, jaws, gill arches, and head muscles are described and figured. Comparisons are made throughout with similar structures of Urodeles and certain other frogs, particularly Discoglossus pictus and Kana temporaria. A summary of the characters which Ascaphus shares with the Urodeles is given on pp. 175-7 and with Discoglossus on pp. 177-8. The reader is referred to these lists as an important part of this summary. Noble (1931, &c.) considers Ascaphus (with Liopelma) to be one of the two most primitive living frogs. The findings of this paper are in full agreement with this view. Thus larval Ascaphus is shown to be a persistently primitive ‘link-animal’ whose cranial structures, in almost every case, differ from those of other frogs--often radically--and throw much light on the evolution of the modern-type frog tadpole from the unknown (larval) ancestor. Ascaphus is shown to have more characters in common with the Urodeles than any other frog larva yet described. Most of these are probably a simple retention of an ancestral Amphibian plan which led on to the frogs and Urodeles (contrast the writings of Holmgren and Säve-Söderbergh). Others seem to link these two orders even more closely together. Such are: (1) The presence of ‘urobranchial’ prongs on the basibranchial copula and the attachment to them of Subarcuales obliqui and Eecti cervicis muscles; (2) the presence of a pair of Branchio-hyoideus externus muscles and other similarities of the musculature. The relationship of Ascaphus to the Gymnophiona is far less marked. Ascaphus, however, has remained more primitive than the present-day Urodeles by retaining: (1) a? Vth gill bar, with its Subarcualis rectus and S. obliquus muscles, and (2) four pairs of S. obliqui muscles instead of two. In these points it is, in fact, the most primitive living tetrapod. Ascaphus is, however, somewhat specialized in relation to a sucker mechanism and to a peculiar method of larval progression which it employs. These have led to an exaggerated autostyly of the palatoquadrate which has developed an additional fusion to the anterior tip of the auditory capsule; to a rigid fusion of the central part of the supra-rostral system to the skull; to the general heavy build of the head cartilages and to the great size of several of the mandibular and hyoid muscles; to a general consolidation and widening of parts of the hyobranchial apparatus; to a widening of the posterior jaw cartilages and the development from them of unique posterior spurs. A pre-oral mouth cavity and a long ‘posterior narial tube’ to the inner nostril are also parts of this specialization. Among the frogs Ascaphus is shown to be most nearly related to the Discoglossidae, which appear to have been derived from an ancestor with many Ascaphus-like characters. This is in further agreement with Noble's classification and is particularly true of Discoglossus pictus. Ascaphus is unique among frogs in the posterior position of its splanchnic head structures; see the list on p. 147. A forecast is made of the probable evolution of the moderntype tadpole's jaw system from that of the unknown ancestor and this is diagrammatically summed up in Text-fig. 7, pp. 158-9. Evidence is collected to show that the ‘anterior basal process’ (= commissura quadrato-cranialis anterior) is not an ethmoidal structure by origin, as has been held up to now, and consequently Säve-Söderbergh's use of it to explain an ethmoidal structure in a Stegocephalian Amphibian is criticized. An account of the muscles has been given in summary form on pp. 126 to 146 and cannot be further condensed here. But it may be noted that Edgeworth's theories (1935) of the primitive muscular content of a single branchial segment break down when applied to Ascaphus. It is now probable that a single segment could simultaneously contain a Subarcualis rectus, a S. obliquus, and a Transversus ventralis muscle. Further, Edgeworth's term ‘Transversus ventralis II’ must be changed to ‘S. obliquus II’ in the frogs and his ‘S. rectus IV’ must probably be changed to ‘S. recti IV, III, and II’ in the Urodeles.

Memoirs: The Development of the Skull of Scyllium (Scyliorhinus) canicula L

1. The development of the skull of Scyllium canicula has been studied from the first appearance of cartilage, through thirteen stages, up to the point at which the main features of the adult skull have been acquired. 2. The parachordals are the first elements to chondrify, and evidence is presented confirming Goodrich's observations concerning the visible traces of metameric segmentation of the metotic region of the paraohordal. 3. The auditory capsule chondrifies from the first in continuity with the parachordal, to which it is attached by the anterior basicapsular commissure. 4. The polar cartilages have not been found separate, but they appear as nodules of cartilage attached to the under surface of the anterior ends of the parachordals. 5. The orbital cartilage becomes attached to the parachordal by means of the pila antotica, and to the trabecula at the base of the lamina orbitonasalis by means of the preoptic root. 6. The hind wall of the pituitary fossa is formed in a complex manner, from a postpituitary commissure between the polar cartilages, and a pair of inwardly directed processes from the foremost ends of the parachordals forming the dorsum sellae. There is also a precarotid commissure, enclosing the carotid arteries in a foramen between itself and the postpituitary commissure. 7. The basicranial fenestra has been demonstrated. 8. Arguments are given for rejecting Allis's view that the so-called basicranial fenestrae throughout the craniates are not homologous. 9. Attention is called to the vacuity in the median wall of the auditory capsule through which the posterior canal bulges, and to the fact that this vacuity is not to be confused with the foramen endolymphaticum. 10. The relations of the glossopharyngeal nerve are described, and it is shown that its apparent passage through the cavity of the auditory capsule is to be ascribed to the fact that the lamina hypotica of the parachordal acts as a false floor to the auditory capsule, the true floor of which is in this region unchondrified. 11. The problem of the relations of the jaws to the brain-case is reviewed in the light of recent investigations, and a reasoned classification is attempted. 12. It is noticed that chondrification is delayed in embryonic material collected from Naples, as compared with material of similar size and degree of development obtained from Plymouth.

Memoirs: The Early Development of the Chondrocranium of Salmo fario

1. The parachordal of Salmo fario was not observed to chondrify in two separate portions, anterior and posterior. 2. No separate pole cartilages were found. 3. The first part of the auditory capsule to arise is in the region where the hyomandibula will become attached to it. 4. The hyomandibula, symplectic, and ceratohyal arise as separate cartilages. 5. The hypohyals, basihyal, and copula arise as separate cartilages. 6. The ceratobranchials, hypobranchials, epibranchials, and pharyngobranchials (at least the anterior) arise as separate cartilages. 7. The lateral commissure is formed from the post-palatine process, the prootic process, and cartilage representing the basitrabecular process. 8. The taenia marginalis (or orbital cartilage) arises separately. 9. Rudimentary basal and otic processes are carried on the pterygo-quadrate. 10. The olfactory nerve comes to traverse the orbit as a result of the relative forward displacement of the lamina orbitonasalis.

Memoirs: Studies on the Vertebrate Head

It is impossible to summarize the results and conclusions arrived at in this paper completely without occupying too much space. The following are the main points : 1. The skull is remarkably uniform in all vertebrates, the differences being mostly of detail. With the assistance of the conception of a schematic skull, the conditions in all can easily be made out. 2. The view that the ala temporalis is partially homologous with the ascending process is supported. 3. The view that the so-called ‘Alisphenoids’ of Teleostomes, reptiles, and birds are not homologous with the mammalian alisphenoid is supported. 4. The basitrabecular process has been traced throughout the fish. 5. The morphology of the trigemino-facialis chamber and myodome is described. 6. Allis's theory of the trigemino-facialis chamber is discussed. 7. The lateral commissure is not to be confused with a prefacial commissure, and it is not homologous with the otic process. 8. Distinct polar cartilages are found in Scymnus. 9. In Scymnus the pila prootica is shown to arise behind the polar cartilage from the anterior region of the basal plate. 10. The dorsum sellae, acrochordal, or prootic bridge are not part of the original skull-floor. 11. In Amia (41 mm. stage) well-marked basal and otic processes are carried by the pterygoquadrate, which extend nearly but not quite to the basitrabecular process and auditory capsule respectively.

VIII.— The development of the auditory apparatus in Sphenodon punctatus ; with an account of the visceral pouches, aortic arches, and other accessory structures

An investigation of the development of the inner ear of Sphenodon was suggested to me by Prof. Dendy during the spring of 1913, and the present paper records the results of the consequent research begun at King’s College in the summer of the same year. At an early stage of the work it became evident that a study of the inner ear, isolated from the structures intimately associated with it, would be neither conclusive nor complete. The scope of the investigation was therefore extended to include the development of the pharynx, the auditory capsule, the middle ear, and the nerves and blood vessels of the auditory region.