JtUy 2, 1874] 



NA TURE 



167 



cumference of the earth, we may assume that the longi- 

 tude of the major axis is constantly changing and pro- 

 gressing from west to east within certain limits, and then 

 returning from east to west ; in other words, oscillating 

 through a determinable space. 



1 have ventured to bring this interesting subject under 

 the notice of the readers of Nature in the hope that it 

 may receive the attention which it appears to merit, and 

 that satisfactory illustrations will be forthcoming to show 

 that the differences between the equatorial major and 

 minor axes of the earth are competent to explain or throw 

 light on many disputed points in geological inquiry, and 

 to lead to a rational solution of some difficult problems. On 

 the other hand, it does not appear unreasonable to suppose 

 that known geological facts may serve to point out a 

 line of investigation which may lead to a more correct 

 knowledge than we appear to possess at present of the 

 figure of the earth, the probable changes which are slowly 

 taking place, and the relation which these bear to geolo- 

 gical inquiry. HENRY Y. HiND 



Windsor, Nova Scotia 



REPORT OF PROF. PARKER'S HUNTERIAN 

 LECTURES "ON THE STRUCTURE AND 

 DEVELOPMENT OF THE VERTEBRATE 

 SKULL"* 



V. 



WHEN the investing bones, mentioned in the last 

 paper, are removed, the chondro-cranium of the 

 axolotl is seen to have a far lower structure than that of 

 the salmon. The hinder part of the skull-floor is consti- 

 tuted by a flat plate of cartilage (Fig. 13, B.O) formed 

 from the investing mass, and answering to the basi- 

 occipital, but unossified. From this rises up on each 

 side a narrow cartilaginous pedicle, which, uniting above 

 with its fellow, forms the occipital ring inclosing the 

 foramen magnum. An ossification — the exoccipital — is 

 formed on each side of this arch where it bears the occi- 

 pital condyles ; but, as in all amphibia, the supra-occipital, 

 like the basi-occipital region, remains cartilaginous. 



From the front edge of the basilar plate proceed two 

 caitilaginous rods, uniting between the nose capsules as 

 an expanded inter-nasal plate (I.N) and rising up to form 

 the walls of the brain-case, but leaving its floor and roof 

 to be covered in by the investing bones— the parietals and 

 frontals above and the para-sphenoid below. These rods 

 are, clearly, the very slightly altered trabeculK ; they bear 

 a single pair of ossifications, placed considerably in front 

 of the optic foramen, and answering to the lateral elements 

 of the " OS en ceinture" or "girdle-bone" of the frog. The 

 nasal capsules, situated immediately outside the expanded 

 cornua trabecule (hypo-trabeculars), arenas far apart as 

 in the ray. 



The auditory capsules are largely cartilaginous, but 

 contain three bones— the prootic, the epiotic, and a small 

 ossicle nearly filling up a membranous space in the 

 capsule between the prootic and opisthotic regions ; the 

 space is the first appearance oi a.fi/n-s/m ova/is,t.he bone 

 of a staples, so that in the tailed Amphibians is seen the 

 earliest foreshadowing of the delicate apparatus by means 

 of which vibrations of the air are communicated to the 

 membranous labyrinth. The apparatus is, however, in a 

 very rudimentary condition, there being neither tympanic 

 membrane nor external meatus, and the stapes being con- 

 nected, not with a chain of ear-bones, but with a band of 

 fibres, the stapedio-suspensorial ligament (s.s.l), which 

 unite it with the hinder part of the suspensorium. 



The upper end of the mandibular arch is not let down 

 to a considerable distance from the skull like that of the 

 salmon, but forms the whole of the suspensory apparatus 

 of the lower jaw, thus taking on the function performed 



* Continued from p. io8. 



in the fish by the proximal portion of the hyoid arch. 

 The suspensorium is a stout cartilage sloping downwards 

 and forwards, rounded below into an articular surface for 

 the jaw, and divided above into three processes, the pedicle 

 (p) or true apex of the arch, the ascending process (a), 

 and the otic process (o). The two former are coalesced with 

 the hinder ends of the trabecula, the latter with the 

 auditory capsule ; the first division of the fifth nerve passes 

 out between the pedicle and the ascending process. A 

 granular deposit of calcific matter (Ou) in the lower part of 

 the suspensorium is the only representative of the bony 

 quadrate of the fish, the meta-pterygoid region remains 

 wholly unossified. 



The pterygo-palatine arcade is very rudimentary, being 

 represented only by a thin bar of cartilage (Pl.Pt) passing 

 forwards from the front edge of the suspensorium, but not 

 coming into contact with the ethmoidal region. Two 

 bones are, however, developed in connection with this 

 cartilage — the small tooth-bearing palatine, and the enor- 

 mous triangular pterygoid. 



As in the salmon, the lower jaw, stripped of its invest- 

 ing bones, consists of an articular and Meckel's cartilage ; 

 the latter, however, is large and stout, and not reduced 

 to a more slender root on the inner side of the dentary. 



The hyoid apparatus (Fig. 12) is a strong bar of car- 

 tilage connected by ligament with the suspensorium and 

 mandible ; it is divided into cerato- and hypo-hyal, but is 

 entirely unossified, and never comes into relation with the 

 auditory capsule. The branchial arches are four in num- 

 ber ; the two hinder are split up into a long epi-branchial, 

 a short cerato-branchial, and a small wedge-shaped basi- 

 branchial. 



One of the most important points to be noted in the 

 development of the skull is [the formation of the stapes ; 

 this was formerly believed to be the apex of the hyoid 

 arch, but its true nature — as a separated portion of the 

 wall of the ear capsule — has been demonstrated in the 

 frog, and confirmed in the newt, axolotl, and other forms. 

 In the axolotl of about an inch long a cresccntic slit is 

 seen in the auditory capsule, formed by the degeneration 

 of its cartilage into fibrous tissue ; the ends of this slit 

 extend and meet, and thus cut off a circular plug of car- 

 tilage set in a ring of fibre, producing at once the stapes 

 and the fenestra ovalis. 



The investing mass remains long in the condition of 

 indifferent tissue, and even after chondrification has set 

 in the two halves remain separate until a very late period, 

 thus approximating to the state of things found in Meno- 

 branchus and Proteus, in which the two parachordals are 

 permanently united only by fibre. 



The trabecule are at first parallel with the post-oral 

 arches, and only at a comparatively advanced stage come 

 to lie almost at right angles to them, as in the first stage 

 of the salmon. The pterygo-palatine process is very late 

 in its development, arising as a bud from the mandibular 

 arch, and growing forwards towards the trabecule, with 

 which, however, it never actually unites. The minor 

 changes which the arches undergo will not be described 

 here, as they have been worked out at far greater length in 

 the frog. 



VI. Skull of the Frog (Rana temporaria). — As far as 

 its general aspect is concerned, the skull of this well- 

 known Batrachian is by no means unhke that of the 

 axolotl : it presents, however, many important differences, 

 and shows a marked advance towards the sauropsidan and 

 mammalian type. 



Among the most important of these characters may be 

 mentioned the backward slope of the suspensorium (see 

 Fig. 14), the large size of the maxilla audits connection, 

 through the intermediation of a small separate bone (the 

 quadrato-jugal, Q.Ju), with the quadrate, the union of 

 the palato-pterygoid cartilage with the ethmoidal region, 

 the disappearance in adult life of the branchial arches, 

 and, most important of all, the separation of the upper end 



