Paper - The primordial cranium of erinaceus europaeus (1918)

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Fawcett E. The primordial cranium of erinaceus europaeus. (1918) J Anat. 52(2): 211-250. PMID 17103834

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This 1918 paper by Fawcett describes development of the primordial cranium of the European hedgehog (erinaceus europaeus).

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The Primordial Cranium of Erinaceus europaeus

By Edward Fawcett, M.D., Professor of Anatomy in the University of Bristol

  • The expenses of this research were largely defrayed by a grant from the University of Bristol Colston Society’s research fund.


THE specimen from which the model illustrating this communication was made I owe to the kindness of Prof. J. P. Hill, of University College, London. In total length it was 25 mm., and was cut into sections of 25 microns thick, stained before cutting with alum-cochineal, and then on the slide with Mallory’s triple connective-tissue stain.

Being an Insectivore, it was thought of interest to examine it in detail and compare it with the mole.

The cranium may be divided into an axial and an appendicular, or a neural and a visceral part, neither division being quite satisfactory. The former is that more particularly associated with the encephalon, the latter the skeletal basis of the visceral arches. We may therefore consider seriatim the neural chondrocranium, ‘the visceral cartilaginous skeleton, and finally the bones where they are found.

The Primordial Neural Cranium

  • In order to justify this mode of description, several plates are appended. They represent the condition as seen in the 11-mm. mole, 12- and 17-mm. Tatusia, and ?19-mm os taurus.

This is perhaps most conveniently considered as consisting of the following parts, viz. :—

1. A central stem, to which are appended, at more or less constant positions,

2. Appendages to the central stem ;

3. Lateral structures ;

4, Commissures binding these lateral structures together ;

5. Dorsal structures, i.e. structures which lie dorsal to the encephalon and form a cartilaginous roof to the cavum cranii.

1. THE CENTRAL Stem. (Pls. 1, 2.)

The central stem stretches at this stage uninterruptedly from the anterior margin of the foramen magnum to the tip of the nose. As far forwards as the nasal capsule it is much wider than deep; but once it has become included within the nasal capsule, its depth suddenly increases; its width at the same time diminishes, so that from now onwards as nasal septum the depth of the central stem is greater than its width (PI. 5).

Constituent Parts of the Central Stem.—Morphologically the central stem appears to be made up of the following parts from behind forwards, viz.: (1.) a part in some relation to the notochord—the pars chordalis (Pls. 1, 2); (ii.) a part related of the hypophysis and its stomodzal duct—the pars trabecularis (Pls. 1, 2); and (iii) a part which, lying between the optic foramina, then as traced forwards between the orbital cavities, and finally within the nasal capsule as the nasal septum, may be alluded to as a whole as the interorbito-nasal septwm or pars interorbito-nasalis (Pls. 1, 2).

In Talpa (Pl. 22), and in Tatusia (Pls. 16, 17, 18) and Cavia, these parts chondrify independently of one another. Whether they do so or not in Erinaceus has not yet been determined, for want of material; but it is most probable that they do. In the calf (Pl. 13) and man (Pls. 19, 20) the pars chordalis chondrifies independently of the pars trabecularis, but I do not know if the latter is independent of the interorbito-nasal septum.

At the stage now being described, as all these parts are fused together and no histological difference can be made out anywhere in the central stem, their sites of union can only be surmised.

Detailed Description of the Central Stem.—The pars chordalis (Pls. 1, 2) may be looked upon as a quadrilateral plate, wide and concave behind as it forms the anterior boundary of the foramen magnum. The posterolateral angles are fused with the exoccipitals, only the hypoglossal canal indicating any demarcation between the two, and there is no developmental distinction since the exoccipital is a direct outgrowth from the chordal plate; but, for later convenience, ossification taking place as it does independently in the exoccipital and extending medially towards the basioccipital centre, one may speak of this cartilage as the exoccipital.

The lateral margins of the chordal plate are partly free where they look towards the foramen jugulare and partly directly fused with the cochlear capsule; anteriorly the chordal plate is fused with the pars trabecularis, and an imaginary line drawn transversely through the middle of the cochlear capsule may be taken as indicating the site of fusion between the pars chordalis and the pars trabecularis.

The Pars trabecularis (Pls. 1, 2)—This, assuming its commencement to be as stated above, is of large size, and very slightly hollowed to receive from above the hypophysis. It may be regarded as a quadrilateral plate with an imaginary posterior border at the aforesaid junction with the pars chordalis. Its anterior boundary is also an imaginary one, formed by drawing a line transversely through the central stem immediately behind the hinder root of the ala orbitalis (Pl. 1). From its postero-lateral angles on each side are given off the following parts: from behind forwards, first the posterior trabeculo-cochlear commissure, fused with the chordo-cochlear commissure (Pl. 1), next the anterior trabeculo-cochlear commissure (PI. 1) which runs back to the lateral side of the apex of the cochlear capsule (Pl. 1). Between the anterior and posterior trabeculo-cochlear commissures the carotid foramen (Pls. 1, 2) is found. Then. follows the ala temporalis (Pls. 1, 2), which at this stage is fused at its root with the anterior trabeculo-cochlear commissure. The lateral border of the pars trabecularis is now free and forms the medial margin of the anterior segment of the spheno-parietal foramen or fontanelle (Pls. 1,2). In the centre of the pars trabecularis a large circular foramen is met with; this transmits the ~ stomodzal duct and is the cranio-pharyngeal canal (Pls. 1, 2). It is to be noted that the main mass of the hypophysis always lies behind this foramen.

Two cartilages lie below the pars trabecularis, and are developed independently of the neural chondrocranium. These are the cartilaginous masses developed in connection with the pterygoid bone (Pl. 2). Each is a somewhat ovoidal mass whose long axis is directed sagittally. Each is placed infero-medial to the processus pterygoideus of the ala temporalis and separated from it by the vidian (parabasal) nerve. No pterygoid bone is developed at this stage in connection with it, but on its superolateral aspect a dense crescentic mass of connective tissue, which occupies the position one usually associates with the pterygoid bone, is found. This mass, too, lies immediately behind the os palatinwm. The mass of cartilage just described has on its outer side the tendon of the tensor palati muscle, and is evidently the cartilage of the hamulus.

The Pars interorbito-nasalis (Pls. 1, 2,5, 6).—This in Erinaceus is of quite unusual width, and receives at its sides the two roots of the ala orbitalis, between which the optic foramen lies on each side. Perhaps the hinder root or limb of the ala orbitalis is really connected with the pars interorbito-nasalis through the ala hypochiasmata (Pl. 2), but that could not be determined at this stage. Free of the two limbs of the ala orbitalis, the lateral free margins-of the pars interorbito-nasalis now form the medial boundary on each side of the orbito-nasal fissure (Pl. 1), then this interorbitonasal septum becomes included within the nasal septum. The nasal septum will be described in detail with the nasal capsule.

Structures Appended to each Side of the Central Stem

From behind forwards are :— (1) The exoccipital cartilage or pila occipitalis ; (2) The auditory capsule ; (3) The ala temporalis ;

- * (4) The ala hypochiasmata and the ala orbitalis ; (5) The lateral nasal capsule.

(1) The Exoccipital Cartilages (Pls. 1, 2). Each may. be taken as extending from an imaginary line drawn through the medial margin of the hypoglossal canal in an antero-posterior direction.

Each passes backwards and outwards at first, haying a free antero-lateral border which forms the hinder boundary of the foramen jugulare (Pl. 2),

Fig. 1. — Erinaceus ewropeus, Al) the sections are coronal ones.

and a postero-medial border which forms the lateral boundary of the primary foramen magnum (Pls. 1, 2). Beyond the lateral limit of the foramen jugulare, the exoccipital cartilage is projected under the pars - eanalicularis of the auditory capsule in the form of lamina—the lamina alaris (P1. 2), which, for the most part separated by a narrow fissure—the The Primordial Cranium of Erinaceas ewropeus 215

recessus swpra-alaris (Pl. 1 and fig. 3)—from the auditory capsule, is terminally fused with that capsule, so that the fissure above mentioned can only be seen from within, and that only after removal of the lateral sinus. The recessus supra-alaris is itself occupied by dense cellular tissue. At its anterior extremity the lamina alaris is fused with the infero-lateral margin of the pars canalicularis of the auditory capsule, and it projects sufficiently below that region to be recognisable externally as a prdcessus paracondlyoideus (Pl. 2), to. whose under surface the musculus rectus capitis lateralis is attached (fig. 3).

Fig. 2. — Erinaceus ewropeus,

In a coronal section of the auditory capsule (figs. 1, 2) above the point of fusion with the processus paracondyloideus one can see the posterior semicircular canal. Before the hindmost limit of this canal is reached, the exoccipital cartilage has once more freed itself from the auditory capsule and is thus separated from it by a narrow fissure, the fisswra occipitocapsularis inferior (Pls. 3,4, 7, 8), and the paracondyloid process has come to anend. This fissure is of comparatively short extent, because the exoccipital cartilage once more fuses with the pars canalicularis, but this time with the postero-medial aspect of the posterior pole of that capsule, so that a recess is produced between the two, which is visible from the exterior. The region of fusion between the posterior pole of the pars canalicularis of the auditory capsule and the exoccipital cartilage may be termed the occipito-capsular commissure (Pls. 7, 8). Here the exoccipital cartilage comes obliquely to an end (Pis. 4,8). Its medial margin forms a considerable part of the lateral boundary of the primary foramen magnum.

(2) The Auditory Capsule (Pls. 1, 2, 7, 8).

This structure taken as a whole may be described as a truncated threesided pyramid, placed very nearly at right angles with the central stem, but with a slight inclination forwards. Together with the pars chordalis of the central stem, the auditory capsules form the floor of that part of the cavum cranii which lodges the parts derived from the hind brain—a part which is as large as the rest of the cavwm cranii.

Fig. 3. — Erinaceus europeus.

The auditory capsule may be regarded as consisting of two main parts : one, more posterior, forming the basal part of the pyramid, and which, because it contains in its interior the semicircular canals, is termed the pars canalicularis (Pls. 1, 2,3, 4, 7,8); the other, which is directed forwards and medialwards, because it contains mainly the cochlea is the pars cochlearis (Pls. 1, 2,7). The small size of this latter part, and especially that which actually contains the membranous cochlea, is very striking. The auditory capsule is moored to other parts of the neural chondrocranium at certain precise spots; thus, the pars cochlearis is fused along the whole of its medial border to the central stem (Pls. 1, 7), and no basicochlear fissure is present at this stage at all events, in which respect Erinaceus differs markedly from Talpa (Pl. 9). The posterior trabecluocochlear and the chordo-cochlear commissures have fused together to form a common commissure just lateral to the apex of the cochlear capsule. The‘anterior trabeculo-cochlear commissure connects the cochlea with the postero-lateral angle of the pars trabecularis, and at the same time this commissure is fused with the proximal portion of the ala temporalis (Pls. 1, 2, 7). The pars canalicularis inferiorly is fused with the paroccipital process of the exoccipital (Pls. 7, 8), and again, by the inner aspect of its posterior pole, is fused with the anterior edge of the upper end of that cartilage (Pls. 7, 8). From the anterior half of the upper border of the pars canalicularis there projects in an upward direction a thin plate, the parietal plate (Pls. 3,7, 8). This, by its anterior margin, is fused with the orbitoparietal commissure (Pl. 3), which connects the parietal plate thus with the ala orbitalis. The posterior margin of the parietal plate is fused with the supra-occipital cartilage of the corresponding side (Pls. 3, 7, 8), but the under margin of the latter cartilage is separated from the hinder half of the upper margin of the pars canalicularis by a well-marked fissure—the fissura occipito-capsularis superior (Pls. 3, 7, 8), a fissure which at its anterior end transmits the lateral jugular vein and is in itself blocked up by the down-coursing lateral sinus. In the intervals between the various commissures mooring the auditory capsule to neighbouring parts of the chondrocranium, vacuities are met with; thus, antero-lateral to both pars canalicularis and pars cochlearis, the spheno-parietal fontanelle is seen (Pls. 1, 2, 3, 4, 7); anterior to the apex cochlee the carotid foramen (foramen caroticum) (Pls. 1, 3,7). Infero-medial to the capsule one sees the jugular foramen continued laterally asa recessus supra-alaris (Pls. 1, 2, 7,8). Finally, above the posterior pole of the pars canalicularis, between the hinder half of the upper margin of the pars canalicularis and the anterior process of supra-occipital cartilage, is the superior occipito-capsular fissure (Pls. 3, 4, 7, 8).

If we now examine in detail the parts of the auditory capsule, commencing with the pars canalicularis, we find that the Pars canalicularis represents the basal part of the capsule (Pls. 1, 2, 8, 4, 7, 8). It contains in its interior the utricle and the semicircular canals; it owes much of its external form to its contents, as we shall see later. For descriptive purposes we may regard this region as having four surfaces, which from their direction may be termed lateral, anterior, medial, and inferior.

The lateral surface (Pls. 3, 4, 8) is irregularly quadrilateral, having an anterior, a superior, a posterior, and an inferior border. The anterior border is somewhat irregular in outline. Commencing above, one notices a slight projection—the teymen tympani (Pl. 3)—which, compared with that in a much younger stage in Talpa, is very small; below this there is a broad sulcus, and below this a notch which is the outer end of the fossa incwndis (PI. 3), in which, in the model, the processus posterior of the incus cartilage is observed lying. Below this a projection, the crista parotica (PI. 3), is met with, and from the lower part of this there projects in a downward. and a forward direction the processus styloideus (P]. 3). Behind and below the root of the processus styloideus there is a broad notch, through which the facial nerve appears. This notch is in the position of the primary stylo-mastoid foramen, and it may also be taken as at the anterior limit of the inferior border of the lateral surface of the pars canalicularis.

The inferior border, commencing as said at the hinder part of the site of attachment of the root of the processus styloideus, is first notched by the facial nerve, behind which it is notched by the stapedius muscle to form the incisura stapedit; behind, this border is fused with the outer edge of the processus paracondyloideus of the exoccipital, a slight groove (Pl. 8), seen from the lateral aspect, separating the two superficially.

The posterior border (Pl. 8) stretches from the hindmost part of the site of fusion of the aforesaid parts and runs almost vertically upwards to reach the posterior pole of the auditory capsule or cuwpula posterior. In this part of its course it is separated from the exoccipital cartilage by a narrow fissure—the fisswra occipito-capsularis inferior (Pls. 3, 4, 7, 8). At the posterior pole the pars canalicularis is fused with the exoccipital cartilage (Pls. 7, 8).

The superior border’ (Pls. 3, 4, 7, 8) stretches from the posterior pole in an arched fashion as far forward as the root of the tegmen tympani. In its hinder part it is free and forms the lower boundary of the superior occipito-capsular fissure, whilst in its anterior half the superior border gives origin to the parietal plate, which rises vertically here from it. Both this border and the posterior one are rounded, each being formed by the bulging of the contained semicircular canal, the former by the superior v. anterior ;, the latter by the posterior semicircular canal.

The Surfaces of the Pars canalicularis.—The lateral surface (Pls. 3, 4, 8) is quadrilateral ; at its upper margin and for some distance below is a semi-. cylindrical swelling reaching practically the whole length of the upper part of the surface, and caused by the superior v. anterior semicircular canal, therefore called the prominentia semicircularis, superior or anterior (Pls. 3, 7). Along the posterior border of the surface the prominentia semicircularis posterior (Pls. 3, 7) is met with. This reaches from the posterior pole to the neighbourhood of the paracondyloid process of the exoccipital, and from near the lower end of this prominence another of considerable width runs upwards and forwards towards the apérend of the crista parotica and is the prominentia semicircularis lateralis TPls. 8, 8), which is caused by the lateral semicircular canal. Between this prominence and the prominentia semicircularis superior v. anterior is a large hollow, which may be termed the fossa subarcuata superior externa (Pls. 3, 9). This fossa is occupied by connective tissue. No opercular process is developed in connection with the lateral surface, in which respect it is unlike that of Talpa (Pl. 10).

The anterior surface (Pl. .74) is bounded, in the main, laterally by the prominent crista parotica. It commences above, below the tegmen tympani, is below this grooved by the facial nerve—suleus facialis,—and further down, in addition, by the stapedius muscle. As a matter of fact, a large part of the fossa stapedii, which ends below at the incisura musculi stapedii, lodges the stapedius muscle just below the point where the facial nerve turns forward and round the outer side of the root of the processus styloideus.

' The medial surface (Pls. 1, 7; figs. 1, 2, 3) is next in point of size to the lateral surface. It is inclined a little upwards and somewhat towards the middle line. It shows just above its middle a fairly well-marked depression, surmounted by the prominentia semicircularis anterior. This hollow is the fossa subarcuata anterior interna. It contains loose connective tissue, and at some distance from it is the floccular part of the cerebellum, which therefore at this stage does not occupy it. Below this fossa is a large somewhat oval vacuity which leads into the interior of the pars canalicularis and in the recent condition is occupied by the crus commune of the labyrinth and by the ductus endolymphaticus (fig. 3). This, when reduced in size, as it doubtless is at a later stage, becomes the foramen endolymphaticum aqueductus vestibuli (Pls. 1, 7) and conducts the ductus endolymphaticus. Below this vacuity the inferior border of the medial surface is seen. It is rounded, and at its anterior part somewhat prominent, forming here the prominentia utriculo-ampullaris posterior. The upper border of the medial surface is rounded for the most part and formed by the prominentia semicircularis anterior (fig. 1). This ends below the anterior part of the spring of the parietal plate in a prominence, the prominentia utriculo-ampullaris anterior (Pls. 1, 7).

The inferior surface (Pl. 7; figs. 1, 2, 3) might also be termed the infero-medial surface, because it is to a large extent inclined towards the cavum cranii. It forms the roof of the recéssus supra-alaris and to a slight extent that of the foramen jugulare. It is hidden from view by the lateral sinus when that is in position. At its most inferior and lateral part it is fused with the upper aspect of the lateral part of the paracondyloid process. Immediately beneath this surface in the recent condition the vagus, glossopharyngeal, and accessory nerves are seen (fig. 1), and the auricular branch of the vagus is given off in this region. A slight fossa suwbarcuata posterior (Pl. 7; figs. 1, 3) is present.

The Pars cochlearis (Pls. 1, 2, 7).—This may be divided into a cochlear and a vestibular segment (Voit). These two segments contain regpectively the cochlear duct and the saccule. The “vestibular” segment is characterised by the presence of a number of foramina which open into it from the exterior; thus, on the lateral aspect, the fenestra vestibuli (ovalis), closed by the foot of the stapes, is seen. On the inferior aspect a large vacuity, the common opening of the fenestra cochlew (rotunda) and foramen perilymphaticum (aqgueductus cochle) are met with. These two components are beginning to be separated from one another by a spur of cartilage growing from the posterior wall of the common vacuity towards the anterior wall; but when complete separation takes place (if indeed it do) I know not. The part of the vacuity destined to. become the fenestra cochlee is closed by.a dense sheet of connective tissue, evidently the primordium of the secondary tympanic membrane, whilst that part which will bécome foramen perilymphaticum (aqueductus cochlew) transmits veins from the cochlea and the ductus petilymphaticus, which latter at this stage is quite solid (fig. 4). The median wall of the “vestibular” segment of the pars cochlearis shows the internal auditory meatus (Pls. 1, 7), which has already become divided up into an upper and a lower part by a crista falciformis (Pls. 1, 7; fig. 5). ‘The upper part is divided into an anterior foramen for the facial nerve — foramen faciale, and a posterior part—the foramen acusticum superius, through which passes the upper branch of the vestibular division of the auditory nerve, whose branches run to the utricle, the ampulle of the superior (anterior) and lateral semicircular canals, as well as to the upper and hinder part of the saccule. The lower segment of the internal auditory meatus is not at this stage divided up into secondary foramina. The lower division of the vestibular part of the auditory nerve supplying the lower and fore part of the saccule, and ampulla of the posterior semicircular canal, runs with the cochlear division of the auditory nerve through this lower segment of the internal auditory meatus.

Fig. 4. — Erinaceus europeus.

Fig. 5. — Erinacéus europeus,

The upper anterior wall of the meatus auditorius internus is formed by the commissura suprafacialis (Pls. 1, 3, 7)—a bridge of cartilage which stretches from the “cochlear” segment of the pars cochlearis backwards over the genu of the facial nerve to reach and fuse with the pars canalicularis. Before leaving the “vestibular” segment of the pars cochlearis, a word or two may be said regarding that surface of it directed towards the primary tympanic cavity. It is, as has already been mentioned, pérforated by the fenestra vestibuli, which in the recent condition is occupied by the foot of the stapes (Pl. 7; fig. 5). Below this fenestra a large prominence—the promontoriwm—is met with, which indicates the position of the first turn of the cochlea. This is grooved about its middle, and in a vertical direction, by the stapedial artery. From the upper margin of the promontorium a sulcus runs forwards and medially towards the medial side of the apex cochlew;-this is the suleus caroticus; it ends at the foramen caroticum (Pl. 74). It corresponds for a considerable part of its- extent with the sulcus septalis, a sulcus which corresponds itself with the septum spirale in the interior of the cochlear capsule.

Fig. 6.— Hrinaceus ewropeus,

The cochlear part of the pars cochlearis is very small (Pls. 1, 2, 7).1 In this respect Erinaceus agrees much with Talpa (PI. 9), and ‘is in very striking contrast with the cat, in which the cochlear segment of the pars cochlearis is of enormous size; so large, in fact, are the cochlear capsules in the cat that they compress to a remarkable degree the chordal plate (Pl. 11), from which they are separated by a large basi-cochlear fissure, but they nearly meet in the middle line over that plate. The “cochlear” segment in Erinaceus has three surfaces, viz. a large infero-lateral, which is in continuity directly in a forward direction with the corresponding surface of the “vestibular” segment of the pars cochlearis, and

1 I am informed by gamekeepers and by mole-catchers that the sense of hearing is poorly developed in the hedgehog. s The Primordial Cranium of Frinaceus ewropeus 223

is marked by the sulcus septalis and the sulcus caroticus, both of which tend to divide it into a lower medial part corresponding with the first coil of the cochlear duct, and an upper more lateral part which, projecting forward as the cupula or apex cochlex, contains the remainder of the cochlear duct. Opposite the middle of the sulcus caroticus there is a deficiency (Pls. 2, 74) in the cartilaginous wall of the cochlear segment evidently a “pressure” deficiency which is doubtless made good later. Over the outer side of the cupula near its basal part the great petrosal nerve-descends, and after a very short course joins the carotid plexus of the sympathetic accompanying the carotid artery. The superior surface of the “cochlear” segment is small and in part overlain by the Gasserian ganglion, more especially jn its outer half and posteriorly, where the suprafacial commissure is being given off.. The remainder of the superior surface is free and helps to join the floor of the cavum supra-cochleare of Voit. The medial surface is in relation with the hypophysis, a structure of enormous size in Erinaceus (fig. 6). This surface is fused in the whole of its length with the central stem, no basi-cochlear fissure being present (Pl. 7). From the region of the cupula the anterior trabeculo-cochlear commissure runs forwards and inwards on the lateroanterior aspect of the carotid foramen to join the stalk of the ala temporalis.

Fig. 7. — Erinaceus exropeus.

(3) The Ala temporalis (Pls. 1, 2, 3, 7).

This comparatively small cartilage springs from the postero-lateral angle of the pars trabecularis by a narrow stalk common to it and the anterior trabeculo-cochlear commissure. At first it. runs directly outwards ; but once the commissure above mentioned has left it, it begins to expand in a forward direction and forms a, for the most part, horizontally directed plate which breaks up into three processes (Pls. 1, 2, 3, 7), which are from behind forwards a postero-lateral, an antero-lateral, and an anterior. Between the postero-lateral and antero-lateral processes the mandibular division of the fifth nerve leaves the cranial cavity (fig. 7), the notch through which it goes being consequently the homologue of the foramen ovale, immediately below which is placed the otic ganglion. The anterolateral process is especially the site of origin of the upper head of the pterygoideus externus muscle, which arises from its lower aspect and is coincident with it. The anterior process is the forward continuation of the medial thickened edge or processus pterygoideus of the ala temporalis ; it juts forwards between the lower head of the pterygoideus externus and on its medial aspect the greater part of the pterygoideus internus (fig. 8).

Fig. 8. — Hrinaceus europeus.

(4) The Ala orbitalis (Pls. 1, 2, 3; fig. 8).

The ala orbitalis is a large triangular plate of cartilage whose base lies laterally and is included in the-lateral structures enumerated above as entering into the neural chondrocranium. It forms part of the floor of the cavum cranii as well. By its anterior basal angle it is fused with a backwardly prolonged process from the frontal prominence of the pars intermedia of the lateral wall of the nasal capsule, forming the sphenoethmoidal commissure (Pls. 1, 3). Its posterior basal angle is prolonged backwards to fuse ultimately with the parietal plate and form the orbito

Fig. 9. — EHrinaceus europeus.

parretal commissure (Pls. 1,3). The apex of the ala orbitalis is directed towards the central stem (hinder part of pars orbito-nasalis); before reaching the central stem the apical region bifurcates into an anterior and a posterior branch (Pl. 1). The former reaches the central stem in front of the optic nerve ; the latter reaches the central stem—? the ala hypochiasmata—behind the optic nerve, so that between the two limbs the optic foramen is formed. The optic foramen here is really a tunnel (fig. 9) whose floor is formed by the ala hypochiasmata, or at all events what corresponds with that structure in other mammals. The upper wall of the tunnel seems, so far as my experience goes, intrinsic to Erinaceus. It seems to give origin especially to the obliquus superior of the eyeball. The lower wall of the tunnel, the ala hypochiasmata proper, gives origin to the rectus ' system of muscles, especially the inferior and lateral recti. The anterior border of the ala orbitalis is for the most part free, and forms the hinder boundary of the orbito-nasal fissure (Pls. 1, 2, 3), through which the nasal nerve enters the cranial cavity from the orbit to reach ultimately the cribriform plate of the ethmoid. Just lateral to the optic foramen a deep notch is found in the anterior free border of the ala orbitalis (Pls. 1, 3), but it does not transmit anything. The posterior border of the ala orbitalis is free, and forms at once the common anterior boundary of the spheno-parietal fontanelle and that segment of it which, lying anterior to the ala temporalis, is the representative of the sphenoidal or superior orbital fissure and foramen rotundum combined, through which run the maxillary and ophthalmic divisions of the fifth nerve, the third nerve, the sixth, as well as the fourth. It may here be mentioned that the maxillary division of the fifth nerve does not perforate the ala temporalis, so that a foramen rotundum is absent, as is the case in most mammals. The outer surface of the ala temporalis is marked by a horizontal sulcus in which the supraorbital artery lies, down to the level of which reaches the frontal bone.

The Ala hypochiasmata (Pls. 2, 3; fig. 9)—This has already been alluded to as probably the lower half of the optic tunnel, and is well marked in Erinaceus. It gives origin to the rectus system of muscles of the eyeball, and at this stage seems to be associated with the hinder branch of the apex of the ala orbitalis. How it develops in Erinaceus I know not, but in Tatusia novemcincta it is developed independently. Possibly that is its usual mode of development, and recently Kernan has shown this to be the case in man.

(5) The Lateral Nasal Capsule.

This, though truly a lateral appendage to the central stem, will be described with the nasal ‘capsule.

Lateral Structures

These are the ala orbitalis, the parietal plate, and the anterior process of the supraoccipital cartilage. The ala orbitalis has been fully described, and nothing more need be said concerning it.

The Parietal Plate (Pls. 3, 7, 8), already mentioned i in connection with the pars canalicularis of the auditory capsule, is a very simple structure, and may be considered as a quadrilateral plate fixed by its lower border to the anterior half of the upper margin of the pars canalicularis of the auditory capsule (fig. 5). Its anterior margin is free, and helps to form the posterior boundary of the spheno-parietal fontanelle. Its superior margin is likewise free. Its superior margin forms the anterior boundary of the superior The Primordial Cranium of EHrinaceus ewropeus 227

occipito-capsular fissure. Its antero-superior angle is fused with the orbitoparietal commissure, whilst its postero-superior angle blends with the anterior process of the supraoccipital cartilage. It is covered laterally at this stage by the parietal bone, but only in its upper half. The lower half of its outer surface is covered by a thick layer of perichondrium, from which arises part of the temporal muscle.

The Supraoceipital. Cartilage (Pls. 1, 3, 4, 7, 8).—This cartilage is of great interest in Erinaceus at this stage, because it perhaps gives us the key to the morphological history of what will later be alluded to under the name tectum synoticum or tectum posterius.

It may be described as a triangular plate whose apex is directed downwards towards the pole of the pars canalicularis of-the auditory capsule (Pl. 8). Its anterior basal angle is fused with the postero-superior angle of the parietal plate, whilst the posterior basal angle stretches medially over the cavum cranii to meet its fellow in the middle line, fuse with it, and form the so-called. tectum synoticum or tectum posterius, which in Erinaceus is very narrow. The under margin of the supraoccipital cartilage is free, and forms the upper boundary of the superior occipito-capsular fissure. The upper margin is free and somewhat irregular; whilst the lower margin, at first near the apex, connected by fibrous tissue with the oblique upper edge of the exoccipital cartilage and more medially for a short distance fused histologically with it, is then continued medially as the upper margin of the primary foramen magnum. In the calf at the 19-mm. stage (Pls. 12, 13) and at the 40-mm. stage (Pl. 14) the various phases in the formation of the tectum synoticum from the enlarging supraoccipital cartilages of the two sides can be followed out in their entirety. Whether this plan is followed in other mammals remains to be shown. The term tectum synoticum is not altogether a happy one, and had better be abandoned for the term tectum cranii posterius (Pl. 8). Its connection with the auditory capsule is indirect, 2.e. through the parietal plate, and it is also clearly a secondary one. - _In man there are two tecta (Bolk, Fawcett): one a very wide one, the more posterior, therefore called the tectum cranti posterius, from the middle of whose anterior border a processus ascendens arises (Fawcett ; in pig, Mead); the other, the tectum cranw anterius, is very slender and quite isolated, not reaching the parietal plate on either side, nor being in any way connected with the tectum cranii posterius. Recently, I have observed two tecta in the cat: one certainly the ordinary tectum posterius, the other small, median, and anterior to this, which may be an isolated processus ascendens or may be looked upon as a tectum anterius. It seems to be quite clear that this region of the chondrocranium is in a progressive condition, as Gaupp has stated. In Dasyurus viverrinus (Pl. 15) 9°5-mm. stage two bars run across the middle line, but both appear to be parts of the tectum posterius, or has the anterior one reappeared in isolated form as in man and cat? This is scarcely probable.

The Lateral Commissures

These are, from before backwards, first the spheno-ethmoidal (Pls. 1, 3) (of large size), which connects the anterior basal angle of the ala orbitalis with a backward projection from the frontal prominence of the pars intermedia of the lateral wall of the nasal capsule. Next follows the orbitopurietal commissure (Pls. 1, 3), connecting the posterior basal angle of the ala orbitalis with the antero-superior angle of the parietal plate. Finally we may describe the union of the anterior angle or process of the supraoccipital cartilage with the postero-superior angle of the parietal plate as the occipitoparietal commissure (Pl. 3); or of course the tectum posterius, stretching as it does from parietal plate of one side to that of the other, may be looked upon as the commissura posterior.

5. The Nasal Capsule

(Pls. 1, 2, 3, 4, 5, 6).

This is an enormous structure. Its antero-posterior length amounted in the model to 200 mm., whereas the total length of the central stem behind was only 125 mm.

It consists of a central part, the septum nasi, and two lateral appendages (as Fischer says, it may be compared with a double-barrelled gun). When the whole is viewed from above (Pl. 1) it has a very characteristic pearshape, of which the larger end or bulb is placed backwards. The whole capsule is more complete than usual, recalling that of the mole (Pl. 9), but it is relatively not so long. The main openings into it are the large subcerebral vacuity on each side of the septum which, at this stage, has not been bridged over by a lamina cribrosa; the fenestra (incisura) narina (Pls. 2, 3, 4) which is placed rather laterally than apically; and the long fenestra basalis (Pl. 2) which is seen below. A small fenestra dorsalis (Pl. 1) is present just behind the apex of the anterior part of the nasal capsule, recalling somewhat that seen in the mole (PI. 9), but it is more apically placed than in the latter. No foramen epiphaniale could be found after a most careful search, but a small cribro-ethmoidal canal is present.

The nasal septum (Pl. 5) is that segment of the pars interorbito-nasalis which is included in the nasal capsule. It is of great length; is partly subcerebral—say one-third; the remainder is precerebral. The subcerebral part is very narrow from above downwards; posteriorly it is also narrow from side to side (fig. 10); thicker below, however, than above. When traced in the forward direction it rapidly increases in height, its upper border rising in height whilst the lower remains more or less constantly at the same level. The greatest height is reached at the junction of the subcerebral and precerebral parts of the upper border. At the hindmost part of the subcerebral segment of the upper border a cartilaginous bar is given off on each side to connect the septum with the lateral wall of the nasal capsule. This bar I think well to name the tectwm nasi posterius (Pls. 1,5).

Fig. 10. — Hrinaceus europeus.

Fischer has named the corresponding bar in Talpa the planwm antorbitale. That term I think better to use in another sense and for another region. At the junctional region of the upper border of the subcerebral part of the septum with the precerebral part two prominences arise on each side. Perhaps they represent a cartilaginous crista galli. The precerebral part of the upper border of the septum nasi is attached laterally in its whole length to the tectum anterius (Pl. 1; fig. 11), and as each half of this tectum in passing laterally from the septum arches first in an upward direction, it follows that the precerebral part of the upper border of the septum lies at the bottom of a longitudinal median sulcus, sulcus dorsalis nasi (Pls. 1-5). From behind forwards this part of the upper border for two-thirds of its extent slopes downwards and forwards, forming roughly an angle open below of about 135° with the subcerebral part of the border (Pl. 5). -But beyond this point the anterior third runs more horizontally forwards. This part at its anterior end turns. suddenly down at right angles to form the anterior border of the septum, and from its lateral margin the wing-like expansions pass in an arched manner forwards, then outwards, and finally backwards to form the cwpula anterior (Pls. 2, 3,4, 5) or median alar cartilage’ on each side, from which there projects the free lateral edge and about its middle a peg-like process, the processus cupularis or processus alaris medius. The inferior border (Pls. 2, 3, 4, 5) is of great length, and is thicker than either the superior or the anterior border,

Fig. 11. — Erinaceus europeus.

especially in its hinder two-thirds. For about its hinder two-thirds it is comparatively straight and. continues almost uniformly the plane of the under aspect of the central stem behind it, being bent at its commencement only slightly at an angle with the latter; but as one reaches the anterior extremity of its hinder two-thirds it rises upwards somewhat and becomes greatly thickened (Pl. 5); then bending downwards at right angles to its original course it joins the anterior third of the lower border, which is much thinner and appears to bifurcate to form more posteriorly the lamin transversales anteriores, and more anteriorly two triangular plates which are almost a replica of those found in the mole. Perhaps they may be — called processus laterales ventrales (Pl. 2). The apex of each is separated by a narrow fissure, continuous with the lower segment of the fenestra narina, from the processus alaris swperior v. lateralis (Pl. 2). From what has been said, the whole septum viewed from the side has a somewhat triangular form, of which the base is formed by the lower border.

The whole septum is comparatively thin save at its lower border, and in the neighbourhood of the junction of the posterior two-thirds with the anterior third it greatly thickens, and in coronal section has a somewhat pear-shaped form (fig. 12), the larger end of the pear being downwards.

The septum at its lower border (Pls. 2, 5) has numerous important relations. Commencing behind, there are at each side of this border the following structures: first, the lamina transversalis posterior, separated by a narrow fissure from the septum (fig. 10); next, the corresponding lamella of the vomer, which stretches from the lamina transversalis posterior as far as the medial side of the hinder end of the organ of Jacobson; next, the free part of the organ of Jacobson ; next, the medial lamella of the anterior paraseptal cartilage (fig. 13); then a thick band of connective tissue (fig. 12), which stretches between the thick part of the lower border of the septum and the narrow cylindrical stalk of the medial lamella of the paraseptal cartilage and the median part of the hinder edge of the lamina transversalis anterior; next, the lamina transversalis anterior, which i is directly continuous with the septum; finally, the base of the processus lateralis ventralis (fig. 14).

Fig. 12. — Hrinaceus ewropeus.

The lateral part of the nasal capsule (Pls. 6, 3, 4) may be described as consisting of the following parts: a roof, composed of a small tectum posterius ; a large tectum anterius; a lateral wall (paries nasi); a floor; an anterior wall (cupula anterior) ; ; and a posterior wall (cupula posterior).

The roof (Pls. 1, 5, 6) is partly subcerebral and partly (mainly) pre-.

Duct. gland. lat.nas. cerebral. The subcerebral part of the roof is complete posteriorly, forming the tectum nasi posterius,—a bar of cartilage, quite flat as seen from the cavum cranii (Pl. 1), which stretches outwards from the upper border of the subcerebral part of the septum to the lateral wall. The remainder of the subcerebral part of the roof, represented in older stages by the lamina cribrosa, is wanting at this stage. The precerebral part of the tectum is complete save near the apex, where it is perforated by the small fenestra dorsalis (Pls. 1, 5), which in the recent condition is filled with fibrous tissue. and a blood-vessel. In its whole length this part of the tectum (tectum anterius) is slightly convex from side to side, the two convexities ‘ producing the median dorsal sulcus, at the bottom of which the upper margin of the precerebral part of the septum lies. Almost insensibly the tectum passes into the lateral wall or paries nasi (figs. 11, 12; 18, 14).

Fig. 13. — Hrinaceus europeus.

The lateral wall, as seen from the exterior (Pls. 3, 4), shows the three divisions already mentioned in connection with roof, viz. the pars posterior pars intermedia, and pars anterior. These parts are separated from one another by curved sulci, thus—the pars posterior is separated from the pars intermedia by the sulcus lateralis posterior. This is a curved sulcus, convex forwards, which stretches from the upper margin of the lateral wall of the nasal capsule behind the attachment of the spheno-ethmoidal commissure forwards, then downwards, and finally somewhat backwards to .reach the lower margin of the lateral wall. It is not very well marked, especially below, but it coincides in the interior with the main attachment of the first primary ethmo-turbinal. The sulcus lateralis anterior is likewise not very well marked, but it may be traced in a downward and forward direction from the cribro-ethmoidal ‘foramen to the lower edge of the lateral wall.

Of the three divisions of the lateral nasal capsule, the pars anterior is in length almost the equal of the pars intermedia and pars posterior taken together.

The pars posterior commences behind at the. cupula posterior, and is triangular in shape, the apex being at. the said cupula and the base at the sulcus lateralis'posterior. Its upper margin is subcerebral, and here forms the outer wall of the olfactory vacuity. . Its lower margin is sharply defined, and when traced inwards is seen to be continuous with the outer edge of the lamina transversalis posterior. This margin in the complete: condition is in relation with the os palatinum. The lateral surface of the pars posterior is flattened or even slightly hollowed out, and, being in relation to the orbit, is called planum antorbitale; but the planum antorbitale extends beyond this region on to the posterior aspect of the pars intermedia, and it obscures the postero-lateral sulcus somewhat by doing so.

Fig. 18a. — Erinaceus ewropeus.

The pars intermedia is placed between the antero-lateral and posterolateral sulci, and possesses the greatest height of the three parts into which the lateral wall is divided. It shows three prominences, viz. a prominentia superior or frontalis, a prominentia inferior or maxillaris, and between the two in front a prominentia anterior. This last is ill marked. Each of these prominences is caused by a corresponding -hollow on the internal aspect. To the prominentia superior or frontalis the spheno-ethmoidal commissure is attached, while from the front of the prominentia inferior v. maxillaris the inferior oblique muscle of the eyeball arises.

The sulcus lateralis anterior, which delimits the pars intermedia anteriorly, corresponds in the interior with the greater part of that important landmark the crista semicircularis (PI. 6).

The lower half of .the anterior surface (Pl. 4) of the maxillary prominence is covered by the maxilla, and at this stage the hinder part of the frontal prominence is covered by the frontal bone; and as these bones, so far as I know, always have this relation to the prominences in question, I have given the alternative names to them.

Fig. 14. — Erinaceus ewropeus.

The inferior margin of the pars intermedia is slightly inrolled, and forms in its anterior part a portion of the maxillo-turbinal (Pl. 6; fig. 13), which, however, chiefly belongs to the pars anterior.

The pars anterior (Pls. 3, 4) is of considerable length, as has already been stated; but it is of only moderate height, a height which is pretty uniform throughout. Superiorly, it runs into the tectum anterius at a rounded superior border; posteriorly, it is separated from’ the pars intermedia by the antero-lateral sulcus. The inferior border can be divided into three parts; the hinder part, equal in length to the other two combined, is inwardly projected as a shelf, and along its greatest convexity runs the naso-lacrimal duct. Here too the mucous membrane The Primordial Cranium of Erinaceus ewropeus 235

of the nasal sac projects sufficiently low down to be visible from the lateral aspect, but that is not shown in the model. There is no lamina infraconchalis such as occurs in the rabbit (Voit) or in the model of Microtus, from which the mucous membrane has been removed (Faweett).

One may see at some depth the greater part of the anterior paraseptal cartilage as well as the organ of Jacobson, which rests in its concavity (P). 3). The anterior end of this part of the inferior border ends at the lamina transversalis anterior; the next stage of the inferior border is fused with the outer edge of that lamina; a deep gutter, in which the naso-lacrimal duct is lodged, marks the line of junction of lamina with the inferior border (fig. 12). In front. of the lamina the final part of the inferior border becomes free, forming the lateral margin of a small notch, the incisura pretransversalis, through which the naso-lacrimal duct passes to fuse with the mucous membrane of the nasal sac.

The anterior border of the pars anterior forms the hinder margin of the fenestra narina, which in Erinaceus is directly laterally ; it is incurved about its middle, forming a somewhat triangular plate which is the anterior end of the atrio-turbinal (PI. 2).

The fenestra narivna (Pls. 2, 3, 4) is a somewhat dumbbell-shaped vacuity directed laterally. Its anterior border is formed by the cupula anterior, from whose middle ‘there projects laterally and in a somewhat. downward direction a cupular spine. Its posterior border is formed by the anterior margin of the pars anterior, and, as the cupular spine and the anterior end of the atrio-turbinal project towards one another somewhat opposite the middle of the fenestra, it is constricted into an upper and a lower large segment. The fenestra is bounded below by the processus alaris superior, a triangular piece of cartilage which is somewhat bent, so as to be eonvex externally. Behind this plate of cartilage the naso-lacrimal duct reaches the nasal sac.

The floor (solum nasi) (Pl. 2) of the nasal capsule is incomplete, more so than it is in the rabbit or Dasyurus or Microtus. There is a large vacuity in it, the fenestra basalis; moreover, a narrow fissure, representing the septo-paraseptal fisswre of other mammals, intervenes between the anterior paraseptal cartilage and the septum, and between the median edge of the lamina transversalis posterior and the septum. The fenestra basalis is even relatively larger in Erinaceus than it is in the abovementioned forms, because the paraseptal cartilage is incomplete: all that narrow cylindrical part such as is seen in the animals before cited being absent. The structures entering into the solum nasi are the following: behind, the lamina transversalis posterior ;.in front, the lamina transversalis anterior, from whose inner end is projected backwards half way along the medial aspect of the fenestra basalis the bilaminar anterior paraseptal cartilage. These parts may be examined seriatim :—

The lamina transversalis posterior is a triangular plate whose apex is at the cupula posterior, whose base is free, forming the posterior boundary of the fenestra basalis, and whose median end lies along the infero-lateral margin of the septum nasi, separated from it wholly by a narrow fissure— the posterior moiety of the septo-paraseptal fissure (fig. 10). The median edge of the lamina near the cupula is covered by the perpendicular plate of the os palatinum, whilst anteriorly the same edge is covered by and is perhaps being commandeered by the ossifying corresponding lamella of the vomer. The outer side of the lamina is fused with the inferior margin of the pars posterior of the lateral wall, and when viewed from above it can be seen that the second primary ethmoid-turbinal springs from the site of fusion of the two. (I have used the term “fusion” here to express continuity of the two structures, not to infer that they were ever separate.) The region to which the lamina transversalis posterior belongs is one of very great interest, and it has been discussed at considerable length by Eugen Fischer in his description of the skull of Talpa. It cannot be said that anything like settlement has been reached regarding its fate, but what is certain is that the cupula posterior extends backwards, being pushed backwards by the ‘backward growth of the nasal mucous sac. It finally becomes jammed against the point of the apex of the ala orbitalis [(?) ala hypochiasmata], and takes a part in the formation of the cartilaginous body of the sphenoid; and so much is the median part of the body—z.e. the part derived from the hinder end of the pars interorbito-nasalis (presphenoid)—compressed between the cupule of the two sides that it is reduced to a very narrow septum when ossified, which projects in the middle line as the rostrum of the sphenoid and in front as the ethmoidal crest. By what mode exactly the cupula is replaced by bone is not as yet certain, but a glance at the fully-formed sphenoidal turbinal at a time before that has become fused to the rest of the body of the sphenoid gives a facsimile of the cupula as seen from below. Whether, then, the sphenoidal turbinal ossifies from the cartilaginous cupula or from its perichondrium or from the fibrous remnant of the former, and whether by one centre or by many, as Cleland has described, remains uncertain.

The Lamina, transversalis anterior (Pl. 2).—This is of large size and quadrilateral in form; moreover, it is convex downwards and about a horizontal plane. Medially, it is to a large extent in direct continuity with the lower margin of the septum nasi; but as this border is traced backwards it becomes free of the septum, and from its hinder edge a narrow rod The Primordial Cranium of Hrinaceus ewropeus 237

_of cartilage runs backward to connect it with the anterior paraseptal cartilage, to which we will return later. The lateral border is directly continuous with the under edge of the anterior part of the lower border of the pars anterior of the lateral wall of the nasal capsule, and at the line of junction a deep groove—the naso-lacrimal suleus—lodges the naso-lacrimal duct (fig. 12). The anterior border is V-shaped and free; the apex of the V is the incisura pretransversalis, through which the naso-lacrimal duct reaches the nasal mucous sac. The posterior border of the lamina transversalis anterior is free, and forms the anterior boundary of the fenestra basalis. From its medial end, at its junction with the medial border of the lamina, the narrow cartilaginous stalk of the anterior paraseptal cartilage is given off, whereas from its lateral edge an extraordinary cartilage passes outwards almost horizontally, but with a slight curve (whose concavity is upwards) (fig. 12), as far as the outer contour line of the pars anterior of the lateral wall of the nasal capsule. This bar of cartilage I have not met with in any other animal. Between it and the junctional region of the outer edge of the lamina transversalis anterior and the lower edge of the lateral wall of the pars anterior of the nasal capsule, the naso-lacrimal duct enters the naso-lacrimal sulcus from behind, so that the root of this bar conceals the duct from view as seen from below. The bar itself is covered below by the body of the os incisivum. From its direction the bar may be called the processus transversalis (Pl. 2).

The Anterior Paraseptal Cartilage (Pl: 2).—This cartilage commences in a narrow stalk which runs back from the angle of junction of the medial with the posterior border of the lamina transversalis anterior. This stalk is placed at some depth from the general inferior plane of the lamina and main mass of paraseptal cartilage, so that the appearance is that of a deep notch in the paraseptal cartilage. This notch is occupied by the connecting stalk of bone between the main mass of the os incisivum and its “paraseptal” process. The main part of the anterior paraseptal cartilage between this notch and stalk is bilaminar, consisting of a large medial lamella which is outcurved below to form a gutter in which rests the organ of Jacobson (fig. 13). The medial lamellz of the opposite paraseptal cartilages are very closely approximated by their medial surfaces, only a certain amount of connective tissue and the “paraseptal” processes of the ossa incisiva intervening in the anterior half of the inter-paraseptal space (Pl. 2; fig. 18). Each medial lamella is suspended from the side of the lower part of the nasal septum by dense cellular tissue. The anterior end of the bilaminar part projects downwards and forwards and lodges the duct of the organ of Jacobson. This duct, distinguished from the organ itself by the different character of the epithelium lining it, ends ultimately at the inner side of the middle of the naso-palatine duct. The body of the organ projects backwards beyond the hindmost limit of the paraseptal cartilage for a short distance (PI. 5), and it is in the space between the two “organs” that the anterior ends of the vomer appear (PI. 2).

The Medial Aspect of the Lateral Wall of the Nasal Capsule (Pl. 6).— This, like the lateral aspect, may be divided into three parts, and these parts are much more readily distinguished from one another from this aspect. The parts are as before: a pars anterior, a pars intermedia, and a pars posterior. The pars anterior is only imperfectly separated from the pars intermedia by a crest, the crista semicircularis, which stretches from above in the region of the cribro-ethmoidal foramen, which has perforated it, in a downward and forward direction for half the depth of the lateral wall of the capsule; the crest then becomes very low, running downwards and backwards to end in the lateral wall of the maxillary recess. This lower part of the crista semicircularis may be looked upon as the representative of the processus uncinatus, when that exists, of the later ethmoid.

The pars intermedia is the deepest segment of the lateral wall. It is bounded behind by the first primary ethmo-turbinal, and reaches back to the cupula nasi posterior.

Considering these parts now in detail, and commencing with the pars anterior, it may be said at once that it is by far the longest segment. It is roughly quadrilateral in outline, deepest behind, narrowing about its middle to again deepen somewhat in front. Its upper border stretches from the upper end of the crista semicircularis as far as the upper edge of the fenestra narina, and is slightly concave on its upper aspect. It is thickest behind. Its lower border or boundary is formed of several parts: in front, by the processus alaris inferior; behind, that of the lamina transversalis anterior, which is here upcurved to form a large part of the atrioturbinal; behind the lamina transversalis anterior the lower border is formed by the maxillo-turbinal for a considerable distance—in fact, in almost the remainder of its extent; its final part posteriorly is formed by the lower edge of the recessus glandularis, of which more will be said later. The anterior boundary is short, and its middle is swung medially in the form of a triangular plate which forms the commencement of the atrio-turbinal. The posterior boundary or border is only well marked in its upper half, where it is formed by the crista terminalis.

The general medial surface of the pars anterior is markedly concave from above downwards, but from end to end shows about its middle a slight convexity.

This region shows us three turbinal cartilages, which are the atrio-turbinal, the maxillo-turbinal, and the naso-turbinal. The atrio-turbinal (P]. 6) commences anteriorly as a triangular inrolling of the middle of the posterior wall of the fenestra narina. At the middle of its base a small vacuity is seen; the lower basal angle of the triangular plate is continuous with the ridge on the upper aspect of the lamina transversalis anterior caused by the sulcus naso-lacrimalis above described, so this ridge is a part. of the atrio-turbinal. Posteriorly the atrio-turbinal is directly continued ‘into the maxillo-turbinal without any notch of separation such as exists in the rabbit (Voit) and the water-rat (Fawcett). The mazillo-turbinal (Pl. 6) is the medially-rolled lower edge of the pars anterior behind the plane of the lamina transversalis anterior. It may in this case be regarded as the direct backward continuation of the atrio-turbinal. It does not quite correspond with the whole of the lower free border of the pars anterior, which lies posterior to the lamina transversalis anterior. If that border be traced backwards with the microscope, section by section, it will be found that the mucous membrane which covers it, and which forms the actual conchal projection into the nasal cavity, gradually dies away and ceases to project at a spot perpendicularly below the lower end of the crista terminalis. The naso-turbinal (Pl. 6; fig. 18) is of small size, and may be traced forwards from the front of the lower end of the crista semicircularis about midway between the upper and lower borders of the medial surface of the lateral wall of the nasal capsule. Unlike that of the rabbit and of the water-rat, it is attached by its whole length to the lateral wall, and at this stage reaches from the crista semicircularis only one-third of the way towards the anterior margin of the lateral wall (Pl. 6). It partially divides the cavity of the nose into an upper and a lower channel. The lower channel has been named in the rabbit the sulcus supraconchalis (Voit)... It lodges here a considerable part of the lateral nasal gland.

The pars intermedia (PI. 6) is entered by a crescentic somewhat wide fissure. Anteriorly it is imperfectly cut off from the pars anterior by the crista semicircularis, but below that crest it is continuous with the pars anterior through the recessus glandularis. Posteriorly it is limited by the first primary ethmo-turbinal, which overhangs its medial side to a very considerable extent and so reduces the entrance into the general nasal cavity to a crescentic fissure. Below, the pars intermedia is bounded by the junction of the first ethmo-turbinal with the lower border of the lateral nasal wall; whilst above, the pars intermedia opens into the cavum cranii through the large olfactory vacuity.

The general concavity of the pars intermedia is divisible into a series of recesses, of which the main ones are the recessus superior v. frontalis and the recessus inferior v. maxillaris. These recesses are imperfectly separated from one another by the anterior root of the first ethmo-turbinal. In front of this root they communicate with one another and form the point of communication; a small but somewhat deep recess, the recessus anterior, projects forwards under cover and therefore to the lateral aspect of the lower half of the crista semicircularis proper. A fourth recess, but very shallow, is found at the antero-inferior part of the recessus maxillaris ; this recess, the recessus glandularis (fig. 11), is continuous posteriorly with the recessus maxillaris and anteriorly with the sulcus supraconchalis of the pars anterior. These various recesses produce corresponding elevations on the exterior of the pars intermedia, but these are not very readily distinguished on that surface, either because the model is not so well made as it might be or because the corresponding prominences are not well marked.

The recessus frontalis v. superior (Pl. 6) is of large size; freely communicating above with the cavum cranii, overlapped medially by the upper half of the first primary ethmo-turbinal, and below partly shut off from the recessus maxillaris v. inferior by the anterior root of the turbinal just mentioned, it communicates anteriorly with the recessus anterior, and below, in front of the anterior root of the first primary ethmo-turbinal, with the recessus inferior. Its outer wall is marked by one low frontal turbinal which divides it imperfectly into an upper and a lower channel. A special bundle of olfactory nerves arises from the mucous membrane lining the frontal recess and enters the olfactory bulb. The recessus maxillaris is a large and deep recess lying under cover of the lower part of the first ethmoturbinal and below its anterior root; it is crossed in front of its middle by a low-curved ridge in continuity above with the crista semicircularis and on the outer wall of the recess. This ridge, which I have before mentioned as being probably homologous with the root part at all events of a processus uncinatus, cuts off from the recessus. maxillaris a part in front and below in which is lodged the lateral nasal gland (fig. 11); and the actual fossa in which the gland lies is the fourth recess of the pars intermedia, viz. the recessus glandularis. This recess, as has been before mentioned, is directly continued into the sulcus supraconchalis.

The pars posterior v. ethmo-turbinalis is characterised by the presence in it of well-marked ethmo-turbinals. These in Erinaceus are two in number at the stage modelled. In general outline it is quadrangular in form, having therefore four borders, which are a superior, an inferior, an anterosuperior, and an antero-inferior. ‘The superior and inferior borders meet at an acute angle posteriorly—at, in fact, the cupula posterior. The superior border is in great part free, and forms the posterior boundary of the orbitonasal fissure. At its inner end it is, in its upper three-fourths, fused with The Primordial Cranium of Hrinaceus ewropeus 241

the nasal septum and only artificially displayed by section. The lower part is free and directed towards the septum nasi—separated from it, however, by the posterior moiety of what has been previously called the septoparaseptal fissure. The inferior border in its anterior half is formed by the lower edge of the lateral wall of the pars posterior, in its posterior half by the inner edge of the lamina transversalis posterior. The antero-superior border is formed by the upper half of the free edge of the first primary ethmo-turbinal, the antero-inferior border by the lower half of the free edge of the same turbinal. Two turbinals are found in connection with this region which from before backwards are the first and second primary ethmoturbinals (I use the term primary in the sense of priority of development). At this stage there are no secondary ethmo-turbinals. By means of the second primary ethmo-turbinal the general cavity of the pars posterior is divided into two meatiis, viz. a superior or posterior behind the second primary ethmo-turbinal and an inferior or anterior in front of it.

The primary ethmo-turbinals (Pl. 6), as has been said, are two in number, viz. first and second. ‘The first primary ethmo-turbinal is of large size, and extends between the upper and lower borders of the pars posterior. It is attached to the lateral wall by three roots, viz. an upper, lower, and an anterior, all of which, with the exception of the anterior, are continuously attached to the outer wall. The anterior root is bridge-like, being attached only at its anterior and posterior extremities. It runs forwards into the pars intermedia and incompletely separates it into the recessus frontalis and the recessus maxillaris. The upper and lower roots are much in the same continuous line, attached to the lateral wall, a line of attachment which is indicated on the exterior by the sulcus lateralis posterior. From these roots of equal length the main plate is formed which stretches from upper to lower borders of the pars posterior; the medial surface of the plate so arising forms a large part of the lateral wall of the pars posterior, and the free edge of the plate, which looks forwards as well as a little medialwards, forms the most anterior limit of the pars posterior. This free edge really consists of about three equal parts, joined at two angles, of which the lower is the more prominent. The upper part of the free edge is almost horizontal and directed inwards and forwards. The next part bends downwards and forwards to the angular projection above mentioned, whilst the lower part of the free edge runs downwards and somewhat backwards to the lower edge of the lateral wall of the nasal capsule. It is the angle of junction of the middle and lower parts of the free border which constricts the opening into the pars intermedia. The medial surface of the first primary ethmo-turbinal is marked by a faint ridge which runs downwards and forwards and is a hint at a subsequent bilamellar condition of this turbinal, such as frequently exists in other animals. It would seem from the specimens at my disposal that that unilamellar condition is the primary one ontogenetically and phylogenetically.

The second primary ethmo-turbinal is almost a replica in small form of the first, but it has no anterior root, and it shows no sign of being bilamellar. Its root stretches from the upper free border of the pars posterior to the junction of the lamina transversalis posterior with the lower edge of the lateral wall of that region (Pl. 6; fig. 10). Its anterior free edge repeats in smaller form that of the anterior edge of the first primary ethmo-turbinal. By it the cavity of the pars posterior is divided into two meatiis, and it develops later than the first ethmo-turbinal. It is likely that it owes much of its development to the backward growth of the nasal sac. Whether more than two primary ethmo-turbinals are developed in Erinaceus, I know not.

The position of the ethmo-turbinals, especially the first, and of the crista semicircularis strongly suggest that these structures play an important part in the modelling of the nasal capsule, and. that they, by acting as strengthening rods, as it were, or internal buttresses to this wall, prevent its being outpouched at their sites of attachment; hence, as the nasal sac grows it tends to cause the lateral wall of the capsule to bulge outwards at three spots, viz. in front of the crista terminalis, between it and the first” ethmo-turbinal, and behind the first ethmo-turbinal. In this way the various divisions of the exterior are brought about.

Morphology of the Parts of the Solum Nasi.—Some remarks may be made regarding the morphological history of certain structures forming the solum nasi, more especially of the lamina transversalis anterior, the paraseptal cartilages, and the lamina transversalis posterior. In the majority of mammals below man, perhaps in all, the lamina transversalis is present, and in the majority it connects the septum with the lateral wall, a true zona annularis being formed; but in Lepus this lamina is stated by Voit—and I contirm his statement—to be separated from the septum by a narrow fissure.

The posterior paraseptal cartilage seems to be present in some form or other in all mammals hitherto examined. Its presence is usually denied in man, but in a model made by me of the nasal capsule of a 65-mm. embryo, it is certainly present, though small. It is formed by the hollowing out of the planum antorbitale due to the backward growth of the nasal sac, and the floor of the hollow is the lamina. Its form is usually triangular, with base forwards and straight; but if concave, its inner basal angle projects forwards as the posterior paraseptal cartilage. The anterior paraseptal cartilage in the lower mammals commences anteriorly at the inner part of the hinder border of the lamina transversalis anterior by a transversely or vertically deep root, depending upon the animal; it grows backwards by the side of the lower part of the septum and ends posteriorly in a sharp point close to the inner end of the posterior wall of the nasal capsule. When that wall comes to be hollowed out and thrust back by the backward growth of the nasal sac, the lamina transversalis posterior is formed as the floor of the hollow and the posterior end of the anterior paraseptal cartilage fuses with its inner basal angle; by the still greater thrusting back of the posterior wall of the capsule, and perhaps too by intrinsic growth, this junctional region is drawn out into a slender cylindrical rod. Such is the mode of development in Dasyurus; it is similar in Lepus, and in all where there is a complete common paraseptal cartilage. Now this common paraseptal cartilage has on its medial side the corresponding lamella of the vomer, and the vomer tends to invade and surround the narrow cylindrical part and, as we rise in the scale of mammals, to replace it altogether. That condition is well seen in the cat, and in such a condition the vomer makes use of the perichondrial connecting link between the posterior and anterior paraseptal cartilages—in other words, ossifies at its expense. This is very well seen in the ferret and in man. Meanwhile certain changes are taking place in regard to the anterior paraseptal cartilage. As already said, that cartilage arises by an either transversely wide or vertically deep root from the anterior paraseptal cartilage. In Dasyurus it is wide transversely, in the ruminant it is deep. But in Erinaceus and Talpa the commencement of this cartilage is quite narrow; it looks in fact, as seen from the side, as if there were a large notch in it below. This notch is occupied by the commencement of the paraseptal process of the premaxilla, which process is continued backwards along the median side of the anterior paraseptal cartilage, which behind the premaxillary notch has become bilaminar. When we examine the anterior paraseptal cartilage in the ferret and in the cat, we find that the narrow connecting piece above the paraseptal process of the premaxilla is absent, and the bilaminar part is left stranded by the side of the lower border of the septum, in direct continuity with neither lamina transversalis anterior nor with the posterior paraseptal cartilage (if that exists). Its isolation has in each case been brought about by the presence of bone. It still retains the bilaminar form, and the organ of Jacobson rests in the hollow between these lamine. When we reach man, not only has the anterior paraseptal cartilage become isolated as in the cat or ferret, but it has lost its lateral lamella, and it no longer retains any relation to the organ of Jacobson, for that lies stranded high up on the septum nasi. So complete is the separation between paraseptal cartilage and organ that Michalkovics supposed that the organ is not really the organ of Jacobson, but the duct of a septal nasal gland. There can, however, be little doubt that this structure is the organ of Jacobson.

In man a still greater change has taken place in the cartilage of the solum nasi, for the lamina transversalis anterior has disappeared, so that in him the fenestra narina and the fenestra basalis have run together to form one large vacuity, the rostro-ventral fissure of Gaupp.

The Visceral Skeleton

(Pl. 8).

This consists of, from above downwards, the mandibular arcade, next the hyoid arch, then the first, second, and third branchial arch cartilages.

The mandibular arcade consists, from behind forwards, of the incus cartilage, the malleus cartilage, and Meckel’s cartilage, the two latter being in direct histological continuity with one another. The incus cartilage is of the usual form, with a short posterior process lying in a fossa incudis above and medial to the crista parotica, and a long processus which descends somewhat medially and articulates through the medium of a well-marked meniscus of connective tissue with the head of the stapes cartilage. The front of the body of the incus articulates in the usual way with the head of the malleus cartilage.

The malleus cartilage is massive, and sends downwards and then suddenly medialwards a strong manubriwm,; from the front of the malleus cartilage Meckel’s cartilage passes forwards with a slight bend downwards and finally upwards in a generally convergent direction towards its fellow of the opposite side. It preserves in an unusual degree a cylindrical form in the greater part of its forward course. It soon comes to lie against the medial side of the bony mandible—at, in fact, the root of the processus coronoideus,—and it continues its course onwards on the medial side of the body of the mandible, becoming somewhat flattened from side to side as it nears the anterior extremity of that bone; then, about the spot where the bone comes to an end, the cartilage fuses with its fellow of the opposite side, and the two fused cartilages project forwards for some distance beyond the bone in a somewhat conical spinous process. Nowhere at this stage is the cartilage enclosed by bone, nor does it show any sign of ossification at this stage.

The hyoid cartiluge. This consists of two parts: a long hinder part fused directly to the lower edge of the crista parotica and passing forwards from thence with a somewhat sinuous course; having nearly reached the anterior extremity of the thyro-hyal, it suddenly ends, to be succeeded by an ovoidal cartilage which is clearly the cerato-hyal. The stapes, which developmentally belongs to this arcade, is at this stage freed from any connection with it, and is only remarkable in being perforated by a very large stapedial artery.

The thyroid arcade consists of a large thyro-hyal which posteriorly is directly continuous with the upper hinder angle of the thyroid cartilage ; anteriorly it articulates with both the cerato-hyal and the body of the hyoid (Parker’s basi-branchial).

The thyroid cartilage, or cartilage of the second branchial arch, is of large size, and consists of two small ale fused near the lower part of their medial borders. The postero-superior angle of each ala is directly continuous with the hind end of the thyro-hyal, whilst the postero-inferior angle articulates by a well-marked inferior cornu with the side of the cricoid cartilage. Each ala is perforated by two large foramina, which lie in the same vertical line.

The cartilage of the fifth arch, viz. the cricoid cartilage, is of the usual form of completed cricoid, and articulates in the usual way with the thyroid cartilage and the two arytenoids.

The large size of the thyroid cartilage is in striking contrast to that in the mole, in which the ala of the thyroid is in the form of a cylindrical rod, from which, if Symington be correct, one may conclude that the vocal powers of Erinaceus are much more highly developed than those of Talpa.

The Osseous Skeleton

(Pls. 1, 2, 3, 4).

The following bones are now ossified: the parietals, frontals, nasals, premaxille, maxille, palatines, vomer, squamosals, and mandible.

The os parietale (Pl. 3) is of comparatively large size, covers the upper half of the parietal plate of cartilage, the whole length of the orbitoparietal commissure and a part of the ala-orbitalis as far down as the sulcus for the onward continuation of the supraorbital artery.

The os frontale (Pl. 3) is comparatively small, overlaps the ala orbitalis as far down as the same sulcus, and then passes forwards along the outer surface of the spheno-ethmoida]l commissure as far as the frontal prominence of the pars intermedia of the lateral wall of the nasal capsule, which it covers only to a slight extent posteriorly.

The os nasale (Pls. 1, 3) is very small at this stage, and lies upon the hinder part of the téctum of the pars anterior of the nasal capsule.

The os incisivum (premaxilla) (Pls. 1, 2, 3, 4) is well formed, and consists of a body which underlies the processus transversus of the lamina transversalis anterior. The body gives upwards and backwards from the hinder and outer part of its upper surface a short process, obviously the commencement of the frontal process of the os incisivum, and a gap separates this from the corresponding process of the maxilla. From the medial end of the body of the premaxilla a long paraseptal process (Pl. 2) is given off; this passes at first medially into the notch between the medial lamella of the anterior paraseptal cartilage and the lamina transversalis anterior, no doubt causing that notch, as Fischer observed in Talpa. The paraseptal process now goes directly backwards on the medial aspect of the medial lamella of the anterior paraseptal cartilage, and is so continued for about half the length of that lamella. It is not possible to say whether it ossified independently or not.

The mazilla (Pls. 1, 2, 3, 4) is of large size, and consists of a body with frontal, palatine, zygomatic, and outer alveolar processes. Between the outer alveolar and the palatine process tooth-buds are present. The body is perforated by a very large infraorbital foramen (Pl. 4), through which runs the infraorbital nerve. Above the foramen the broad frontal process ascends over the lower part of the maxillary prominence of the pars intermedia of the nasal capsule, and at the same time over the nasolacrimal duct. The palatine process is of very large size, passes medially and horizontally towards the middle line, forming a floor to the greater part of the fenestra basalis of the solum nasi; from the junction of the palatine process with the body of the maxilla the external alveolar process depends. Between the anterior edge of the palatine process of the maxilla and the posterior edge of the corresponding process or plate of the premaxilla is the primary choana, through whose inner end the naso-palatine duct and the terminal part of the duct of Jacobson’s organ project. The zygomatic process of the maxilla is a great length, and passes backwards half-way under the cavity of the orbit to end in a free pointed extremity. To its medial side tooth-buds are found, so that perhaps the term alveolozygomatic proccss would be a better one for it.

The zygomaticwm is only ossified to the very slightest extent, and no attempt has been made to model it. . It, however, may be seen with the microscope behind the pointed end of the alveolo-zygomatic process of the maxilla. There seems to be some difficulty about the zygomaticum of insectivora. In some cases it is said tu be absent, e.g. Centetes; in others very small; but Fischer, in his description of the model of Talpa, says “the jugal is found lateral to the maxilla, passing backwards from the latter as a cylindrical arch (fig. 2). The infraorbital nerve runs over the attachment of this arch. In the full-grown animal it is attached by two limbs to the maxilla; the upper limb here fails. It has not yet reached the squamosal behind, but small masses of bone in the tissues show its future course.”

In my own model of Talpa (19 mm.) (Pl. 21) there certainly is a cylindrical rod passing backwards from the body of the maxilla below the infraorbital nerve, and there is no upper limb going from it to the maxilla to complete the infraorbital canal. In my Erinaceus model (25 mm.) this cylindrical rod likewise goes back from the maxilla, and has an upper limb completing the infraorbital foramen. But this I have already described as the alveolo-zygomatic process of the maxilla, for I cannot see that it is separate from the maxilla; nor is it so in Talpa, not even at the 15-mm. stage. Then too its relation to the tooth-buds, I think, proclaims its maxillary nature, since some of the alveoli are formed in part of it. The Jugal or malar bone, then, is nearly absent at this stage; what there is of it occupies a little, a very. little, of the gap between the alveolo-malar zygomatic process of the maxilla and the anterior end of the squamosal.

Fig. 15. — Erinaceus ewropeus. Right lateral aspect of adult skull.

In the adult Erinaceus (fig. 15) a quite well-marked zygomaticum is present, but it occupies, perhaps, a somewhat peculiar position. What happens is that the alveolo-zygomatic process of the maxilla articulates with the squamosum, and the zygomaticum is placed lateral to that articulation, hiding it from view as looked at from theside. Both alveolo-zygomatic process of maxilla and zygomatic process of squamosum as they approach one another are bevelled at the outer surface, and in the resulting concavity the zygomaticum rests.

The squamosal (Pl. 4) is a small bone which commences behind opposite the middle of the outer side of the short process of the incus cartilage ; it increases rapidly in height, and perhaps reaches its maximal height opposite the incus-malleus joint. Here its upper margin widens sufficiently to form a surface, over which lie the hinder fibres of the temporal muscle. The bone rapidly diminishes in size as it is traced forwards, and it ultimately terminates opposite the hinder edge of the processus coronoideus of the mandible. For a considerable part of its length it is separated from the condyle of the mandible by the still cellular discus articularis, above and below which no joint cavity is as yet demonstrable.

The palatinum (Pl. 2; fig. 8) is a somewhat curious bone, consisting of a palatine process placed for the most part in front of its vertical plate and only connected with the latter by a narrow stalk, and that to the lower part of its interior edge. The palatine process is imperfectly ossified, and from a common stalk connected with the vertical plate it spreads forwards under the lamina transversalis posterior of the solum nasi towards the palatine process of the maxilla, from which it is, however, separated by a considerable interval. The vertical plate really arches somewhat upwards, forwards, and inwards to reach the infero-lateral aspect of the “central stem,” and stretches forwards from the level of the cranio-pharyngeal canal as far as the under aspect of the hinder part of the cupula nasi posterior. It bounds the hinder part of the naso-pharyngeal duct laterally (fig. 8). On its supero-lateral aspect is placed the spheno-palatine ganglion. From its infero-lateral angle the pterygoideus internus arises. The periosteum, in which the upper edge of the vertical plate is embedded, seems to be practically directly continuous with that of the hind end of the vomer.

The vomer (Pl. 2) consists here of two long narrow lamelle, each of which commences behind at the medial edge of the corresponding lamina transversalis posterior, to which it is closely applied (fig. 10). Where the lamina ceases, the vomer is continued forwards infero-lateral to the septum nasi to the interval between the hinder end of the organ of Jacobson and the septum. Here the two separate plates of which the vomer is formed come to lie very close to one another, and it is here that they will first unite. From its position there can be no doubt that the vomer is primarily a covering bone to the medial edge of the solum nasi—in other words, to the common paraseptal cartilage when that exists and to the lamina transversalis posterior. Its relation to the septum as a covering bone—i.e. when the two lamelle have united below the septum—is clearly a secondary one.

The hinder end of each lamella reaches very close to the vertical plate of the palate bone behind; the anterior end of the vomer is separated by a considerable interval from the hind end of the paraseptal process of the premaxilla.

The mandible (Pls. 3, 4) consists of two separate halves, each closely applied to the lateral aspect of the corresponding Meckel’s cartilage. The constituent parts of each half are a body splitting above into outer and inner alveolar walls, a coronoid process, an angle, and a condyle. The common mass from which angle coronoid process and condyle spring may be termed the ramus. The body is pointed anteriorly, and does not reach so far forward as the end of Meckel’s cartilage ; about a third part of the way back from the anterior end a long oval mental foramen is met with, placed much nearer the upper than the lower border. No sign of any accessory cartilage is met with either at the anterior extremity ar in the coronoid process, nor is any to be observed in the angle. The condyle is composed of dense cellular tissue which contains bone in its core, and over this cellular condyle a discus articularis of wedge-shaped form is recognisable, but no joint cavities are present (fig. 7).

No other bone such as one associates with the craninm is as yet ossified.

Comparison Between the Crania of Erinaceus and Talpa

The differences between the cranial and the visceral skeleton of Erinaceus and Talpa are not many, but some are very striking.

The nasal capsule, especially its pars anterior, is relatively shorter in Erinaceus than in Talpa, and there seems to be no foramen epiphaniale perforating the tectum anterius. That in Talpa is very sinuous and difficult to follow.

There is no opercular process on the pars canalicularis of the auditory capsule such as exists in Talpa (Pl. 15).

The Basi-cochlear fissure is absent in Erinaceus. The cranio-pharyngeal canal remains as a large circular aperture in Erinaceus, but disappears at an early stage in Talpa.

The tectum cranii posterius in Erinaceus is very primitive, resembling much more that of Bos than that of Talpa.

The foramen opticum is surrounded by a cartilaginous ring, of which the lower part is the ala hypochiasmata; in Talpa, owing to the rudimentary condition of the eye muscles, no ala hypochiasmata is present.

As this communication is but part of a series, no attempt has been made to introduce the mass of literature which has made the history of the chondrocranium ; only such references are made as directly bear upon the subject. At the end of the series an attempt will be made to summarise the results, and at the same time to point out more precisely how the results confirm or differ from those hitherto obtained in mammals. All the plates, with the exception of 7a (which is by my former pupil J. L. Delicati) and those bearing my own initials, are by Mr S. A. Sewell. The figures are by myself. For the embryos represented by the plates and figures I am indebted to Prof. J. P. Hill, Prof. F. Wood Jones, Dr G. Barker, and my former pupil Dr J. H. Morgan.

Chief References

Voit, “ Das Primordialcranium des Kaninchens,” Anatomische Hefte, 1 Abteilung, 116. Heft (Bd. xxxviii., H. 3).

Fiscuer, E., ‘Das Primordialcranium von 7'alpa Europea,” Anat. Hefte, Abt. 1, H. 56/57°(Bd. xvii.), 1901.

Bouk, “Entwickelungsoorginge in der occipitalen Region des Primordialcraniums beim Menschen,” Petrus Camper, Deel ii. Afi. 5, 1904.

Fawcett, Various communications to Journal of Anatomy on chrondocranium, especially the reconstruction of the head of a 30-mm. (Bryce) embryo.

Weser, Die Sdugethiere. ,

Fiowsr and Lyppexer, Mammals, Living and Eetinct.

Parker, W. K., Phil. Trans. Roy. Soc. London, 1885. Journ. of Anat.) [PLate I.

__. Cupula ant. imi a EOE dorale,

. — — — Processus alaris sup.

~~ — Sulcus dorsalis.

— — — Os nasale.

ea a st ga Maxilla.

Prom. frontalis. 2. — r ‘onta. — -- Prom. frontalis.

Recess. frontalis. — — —


Comm. sph.-eth. _ _ —-- Os frontale. Eth.-turb. II. _ _

Fiss. orbit. ras,

_ Lam. trans. post.

Tect. nasi post. Ala orbitalis. _

For. opticum.

Cart. pterygd. _ Ala temporalis. Comm. orbit. pariet.. — Pars trabecularis. For. carotic. _ . Parietale.

Pars coch. ~

For, faciale. .-Pars chordalis. Parietal plate. _

fussa subare. int. _ Canal. hypogloss. _ For. endolymph., _—

Cart. exocc._ _

Cart. supraoce, _

Erinaceus ewropeus, Chondrocranium of 19-mm. (Hill) embryo, from above.

=< ----- Cupula ant.

Process. cupularis.

Mark Hill (talk) Fenestra narina.

Proc. lat. vent. 2

»--- Process. alar. sup.

-— Incis. pretrans.

Duet. nas. lac. — - — — _ Sule. naso-lac. and

lam. trans. ant.

~- Proc. trans. Incisivan-—~= ==

Proc. parasep. incis. -—- — — -—--—- Cart. parasep. ant.

--— Max. turb.

Proc, pal. max. — Sule. ant. lat.

Se Prom. max.

—— = Eth.-turb. I. —-—— ‘omer. Proc. zyg. max, ~—-- ;

Som ee Eth.-turb. II.

ee Comm. sph.-eth.

Parietale. ---- Law. trans. post.

~--— Ala orbit. ~-— Pars int. orb. nas. Palatinum, .—. — : 5 ss ; ‘ ~- Ala hypochias.

~-~-— -Ala temp.

Can. hypophys.—~ —; == =-Cart. pteryg.

Squamosal.-— —-~-—-Pars trabec.

» . _Ant. trab. coch. comm. and For. carotic.

Malleus cart. Can. facialis. Crista parotica. ~ Pars coch.

For. tymp. et peri“~~ lymphat. BOUTIUES —-— -Can. hypogl.

Atlas, > ——

Erinaceus europeus. Chondrocranium of 19-mm. (Hill) embryo, from below.

Prom. Font. sph.-par. Comm. sph.-eth. — Sule. lat. post. — Prom

Comm. sph.-par. Sule, ant. lat.

Ala orbit. -Frontale. - -~


Prom, max, — —

Organ Jacobs.

front. Prom. ant.-— Cart. paras, ant. and

semic. Parietal plate.

Ala hypoch, —— — — —

Maxilla, ~~ —

Proc. trans.

Atrio. turb. —

Lam. trans. ant, ——

Sule, naso-lac. __

Fiss. occ.-caps. sup.

Cart. supraoce. _ _ c. ant.

Fenes. _ narina, Proc, cupul.

tProc.alar 7 sup.

~~ Comm. suprafacialis. ~ Tegmen tympani.!

—— Cart. exocc. ~- Fossa subare. externa. -- Prom. semic. post.

. Meckel. " a : a Cartes e - : - Prom. semic. lat. - Crista parotica,

1 t ' 1 (

1 U Mandibula.

Blan -caps»inf. / i™

o er o \}



Ala temporalis. a } Canal, hypogloss. a a

| os Basi-branch | ! Proce. styloid. L Thyro-hyal. |

Ala cart. thyroid. =

Cricoid. Erinaceus ewropeeus. Left lateral aspect of chondrocranium of 19-mm, (Hill) embryo.

Journ. of Anat.)

(Puatr III. Professor Epwarp Fawcett.

, Prom. front. Frontale. : Sule. ant. lat.

Parietale. ' Nasale.

1 ' | Due. nas. lac.


Pars ant. Fen. narina,

4 , Cupula ant.

‘ 1 ' ‘ t i '

' t ‘ t Cart. supraoce. { t

i ' i '

i 1 1 i { i

Proc, alar. sup.

4 Proc. trans, Incisivum. Maxilla, - Cart. Meckel. Fiss. occ, caps. sup. ~~ — i ( Art. staped. - —- i

. Cart. exoce, —- ---= Mandibula. Fiss. oce.-caps. inf. -~--—'

For. mentale.

Proc, paracondyl, — - — ----—

Canalic. inf.

‘ Muse. obliquus inf. Palatinum,

‘ Ala temp.

\ \ ‘

N x * Cerato-hyal.

\ \ « Basi-branchial. Squamosum. Se ‘, . Thyro-hyal. \ Ala. cart. thyroid.


Erinaceus europeus. ight lateral aspect of chondrocranium of 19-mm. (Hill) embryo.

Journ. of Anat.)

(Puare LV, Professor EDWARD FAWCETT.

Erinaceus europeus,

Septum nasi of 19-mm. (Hill) embryo, from left side.

Proce, cupul, ---, .

Fen. dorsalis.

~-~-- Sule. dorsalis.

Atrio-turb._--- Lam. trans, ant..---. aero Tect. nasi ant.


Cart.parasep. ant. - -- Organ Jacobs. -= = Sept. nasi (pars pre cere). )

Vomer. -~

oom ‘lect. nasi post.

Journ, of Anat.)

(PuaTE V.

Erinaceus europeus.

Medial aspect of left half of nasal capsule of 19-mm. (Hill) embryo,

Cupula nasi post. ~

Lam. trans. post.

Eth.-turb. IT. Eth.-turb. I. (radix inf.).

Eth.-turb. I, .----~ Recess, max. ~~

Recess. gland, -- -~ Proc. uncinatus, ----- Recess. supraconch, — Mark Hill (talk) Max. turb, ---- Proc. lat. inf. Lam, trans. ant. --&

Atrio. turb, -- Proc. alaris. sup.

Tect. nasi post.

Comm, sph.-eth.

~ Fronto-turbinal. Recess. frontalis. Radix ant. eth.-turb, I.

Crista semic. ~ Recess. ant.

Journ. of Anat.)

(Piate VI. Journ. of Anat.)

Canal. hypophys. - - Pars coch. For. carotic. Comm, trabec.-coch. ant.

Pars coch.

For. acustic. inf.

Comm, chordo-coch, For. jugulare.

Pars chordalis.

Canal. hypogl.

Proc, alaris.

Frinaceus europeus.

{Puate VII.

Ala orbitalis.

oe a \

Comm. sph.-eth .—~-- Ala temp.

-~-- Parietal plate.

< ~~ Comm. suprafacialis. -—-- For. faciale.

-- For. acustic. sup.

~ Crista falciformis. , Prom. semic. ant.

Fossa subarcuata inf.

a --- Fiss, occip.-caps. sup.

— For. endolymph.

Tect. cranii post.

Medial aspect of right auditory capsule and environs of 19-mm, (Hill) embryo.

Professor EDWARD FAWCETT. Journ. of Anat.] , (PuatE VIIa.

=------ Ala orbitalis.

- Fontan. sph.-par.

DB oaoe --- Ala temp.

- Comm. suprafacialis. -- Tegmen tymp. For. carotic. ------ Pars cochl. ----- ; & : Sule. facialis. 5 Fossa incudis.

Crista parotica. Stapes.

Proce. styloid. Promontorium. - ‘oss. stapedii

For. jug.

Can. hypogloss. Proc, paracond.

Occ. condyle.

Erinaceus europeus. Under aspect of left half of base of chondrocranium of 19-mm. (Hill) embryo.

Professor EpwarRD Fawcett. Journ. of Anat.) Puate VIII.

Comm. orb. par.

Parietal plate. -- -— Fiss. occ.-caps. sup. -—-~-- —

Prom. semic. ant. ~-- —-—

ee Tect. cranii post. Cart. supraoce. -~- == s : b

Foss. subare. ext.

- Meat. aud. inf.

f - For. endolymph. Prom. semic. lat. . — — ° ;

Prom. semic. post. ---~ For. Sump: et peri lymph. Fiss. oce.-caps. inf. —

Cart. exocc. -—— ~——-~. Can. hypogloss.

Proc. paracond. ---~-----~- ==

Condyle. ---—-—------ Erinaceus europeus. Postero-lateral aspect of chondrocranium of 19-mm. (Hill) embryo.

Professor EDWARD FAWCETT. Journ. of Anat.] : , (Prats IX,

Cupula‘ant. ee

Proc. alar. sup. Fen. dorsal.

Sule. dorsalis. ---~4 Pars ant.----- ---- Incisivum. Nasale. - Maxilla. Snile, ant. Prom. front. ~--For. epiphan. ~- -- -=~. Frontale. For. cribro-eth. Sule. lat. post. -Crista crib.-eth. - Maxilla. Comm. sph.-eth. = PVvouer. Fiss. orb. nas. — Eth.-turb. II..-~— Lam. trans. post.*-~ Ala orb.-- 9 - ‘eee ee Parietale,

Tect. nasi post.-~ For. optic.-— Pars interorb. nas.-- §

Ala temp.

Pars trabec

Cart. Meckel

Comm. sph.-par. Comm. trabec.-coch. ant. Comm. trabee.-coch. post. — Tneus. _

For. faciale

Pars coch

Tegmen tymp.

Fiss. basi-coch, Squamosal.

— Comm. suprafacialis, _. Meatus aud. int. and

Meat. aud. int. Comm. chord coch.

Pars chordalis. Parietal plate. . For. jugulare. For. endolymph. -- ~~ Incis. ant. Fossa subare. int. Can. hypogloss. = - ~ —--- Cart. exoce.

Fiss. occ.-caps. sup.

ee ae Tect. cranii post.

Talpa ewropea. Chondrocranium of 19-mm. (Wood-Jones) embryo, from above.

Professor EpwARD Fawcett. Journ, of Anat.) [Puatx X.

Tectum cranii post. ---~--~~- Fiss. oce.-caps. inf. Fiss.oce. -caps. sup.

Proc. paracondyl.

Parietal plate. ~~ Operculum.

~-~~-- Fossa stapedii.

Tegmen tymp. ~ - ~—~----- Crista parotica.

Incus, ~


sone Proc, styloid. Fontan? sph.-par. = Seance roc, sty

Sph.-eth. comm. Ala temp. _

Parietale. — For, opticum, Cricoid.

Ala orbitalis. - \ \--- Thyroid.

Pars post. Fiss. orb. nasal. . \\__. Basi-branch

. 4

\-- Cerato-hyal.

Sule. lat. post.

Sph.-eth. comm,

Frontale. -~ Prom, front. ~ ~

Sule. ant. lat. -- ~ Prom. maxill.

Maxilla, --- Cart. parasep. ant. -~--Mark Hill (talk) Mandibula.

Organ Jacobs. - --~

Cart. parasep. ant. - 2 ~- Cart. Meckel.


Pars ant. ~

Proce, alaris. sup. Fen. narina. Cupula ant, -------- ‘

Professor Epwarp Fawcett,

~ Cart. arytenoid.


Left lateral aspect of chondrocranium of 19-mm. (Wood-Jones) embryo.

Talpa ewropea. Journ, of Anat.)

Frontale. Mark Hill (talk)

war cne Comm, sph.,-eth. ae Crista semic.

Pars interorb. nasalis.

~~ Eth.-turb. I.

— . Tect. nasi post. --- Oculus.

Ala orbit.

For. opticun. Comm. orb. par. Muse. rect. lat.

_ Ala temp.

Ala temp. _ Nervus. maxill.

Fen. hypophyseos. Fontan. sph.-par. Comm. trabee. coch.


Malleus. Pars trabec.

Incus. Pars coch.

For. caroticum. Comm. trabec. coch.

post. Comm. suprafacialis.

Parietal plate, _ Canal. facialis

For. acustic. sup. For. acustic. inf. Hiss. basi-coch.

Comm, chordo-coch, For. endolymph. -~Chorda dorsalis.

Sinus lateralis. _—-Canal. hypogloss.

y__-Cart. exoce.

————ok For.-magnum.

~ =~. Tect. cranii post.

Felis catus, Chondrocranium of 32-mm. (Hill) embryo, from above.

Professor EDWARD FAWCETT. Journ. of Anat.)

-- Cart. supraoce,

+~~—- Caps. aud,

Parietal plate. -- ----- Ala temporalis. --------~-~

Ala hypochiasm, --- --~ _L

Pars posterior.

Comm. sph.-eth. (ant. part).

Pars anterior, -——------- Professor EDWARD Fawcett.

—~----—— Cart. exocc.

{Pate XII,

Left lateral aspect of chondrocranium of 19-mm. (Wood-Jones) embryo.

Bos taurus. Journ. of Anat.) (Phare XIII.

~ reese Tect. nasi ant. Prom. front.

——a-- Fiss. orb. nas

~--Ala orb.

~-Cupula nasi post. A


+-Pars interorb. nasalis.

y ~~ For. optic.

~- Ala hypochiasm.

~- Comm. orb. pariet. =-- Fiss. trabec. sept.


~--Ala temp. Mark Hill (talk) Pars trabecularis. For. carotic. .. Font h iet: F : ~~-Fontan. sph. pariet. Fen. basi-cran. . - Parietal plate.

- Comm. suprafacialis.

Nerv. facial. -- Foss. subare. int, —

Duct. endolymph. ~

Pars chordalis. ~~

~---Can. hypogl.

eee Cart. supraoce.

onioceeuars Cart. exoce.

Bos taurus. Upper aspect of chondrocranium of 19-mm. (Wood-Jones) embryo.

Professor EDWARD FAWCETT. Journ, of Anat.] : {PuaTEe XIV.

Cart. supraoce.-- -- ----- 4 sca on == comeee Cart, EXOCC.

Fiss. occ.-caps. sup. -- ----- ~ Mark Hill (talk) — -Fiss. oce.-caps. inf.

Comm. occ. pariet. -- ~~ ~--~ Cart. exocc.

Prom. semic. ant. _ . Prom. semic. lat.

Crista parotica. ~------ = Condyle. Tegmen tymp. ---—Incus,.— = —- Proc. paracondy. S- For. jug.

Nerv. facialis. Nerv. petros. sup. maj. ---- Nerv. trigem. Mark Hill (talk)

Ala temporalis.

Ala hypochias. ~~ _. Cart. pterygoid.

Ala orbitalis.

For. opticum. - ~~ Pars interorb. nas.

Cupula post. -- G - Palatinun.

Frontale. --- Fiss, orb. nas. -Mark Hill (talk) -— Sule. lat. post.

Comm. sph.-eth. - +-—- Vomer. Prom. maxill.- ~~

Prom. front, -- ~ - --~--. Maxilla.

Prom. ant. - ---~- Sept. nasi. Sule, antilats once p ws For. epiphaniale. - - - ~ ~--- = rea! -----~— Mandibula.

Cart. parasept. ant. — Memb. mucosa. ~ Duct. nas. lac. . ‘eh Lae ------ ~---Incisivum.

Fen. dorsalis. Proce, alaris sup, ---- Memb, mucosa, - --- Fen. ant.

Proc. lat. vent. (ant. end of), - ------- 7


Left lateral aspect of chondrocranium of 40-mm. (Wood-Jones) embryo.

Bos taurus. Journ. of Anat.] : [PuatTE XV.

Fen. narina. = -- ~.

Proc, alaris sup.

Fen. dorsalis.

Pars ant. _

Incisivum, -_ Nasale. ___

Maxilla. - For. mentale.

Sule, ant. lat. ---- Cart. Meckel.

Pars intermedia, --~ ‘ ~--- Mandibula.

Frontale. ---- - .-~-- Cerato-hyal.

«-- Basi-branch.

y _.._ Thyro-hyal, oe y-7 Thyroid.

Pars post. -Ala orbitalis, _

/ Oricoid.

Fiss. orb. nasalis.

Ala temporalis. .

§, & 3 o = n a 3 ” 3 = g 5 o wt Sm 3 g 5 A 3 oo 8 i 2 3 <a ° Se 3 — Qo o roo) Q a = g ~ 3 a = 2

Parietale. Steet eee Malleus. Fontan. sph. par. anes Squamosal, _ ~ +--+ Proce. styloid.

Crista parot.

~ Canal. hypogl.

--- Proc. opercularis.

Talpa europea,

Parietal plate... 2-2. 2k / f ~~ Proc. paracondyl.

Fiss. occ.-caps. sup. . Di D. ~Fiss. oce.-caps. inf.

Cart. supraoce. --- Professor EDWARD Fawcett. Journ, of Anat.] , (Puarz XVI.

— Sept. nasi.

-~= Lam. trans. ant.

. Cart. parasep. «ant.

fo - Muse. obliquus

Pars intermed, - ----- use.

M. rect. med. Pars interorb. nas, --- - —

Ala orbitalis. -—-— = —= M. rect, lat.

—--~ M. rect. lat. ?¥For. epioptic. —~-—

For. optic. ._ __ ...- Ala hypochias.

~--- Ala temp. woo r —~- Can. hypophys.

-- For. carotic.

.- Comm. trabec. coch. ant.

-Comm. trabec. coch. post.

-Chorda dorsalis.

Comm. orb. par. --- Pars coch. —

-Malleus. -N. facialis. -Pars chordalis.

Fiss. basi-coch. Foss. stapedii ~Proc. styloideus.

For. jugulare.

Cupula post. Oce. condyle.

caps. aud.

ust meincta. Chondrocranium of 12-mm. (Wood-Jones) embryo, from below. The parts aaotted. are unchondritied, the lamina transversalis anterior and the anterior paraseptal

cartilages are procartilaginous.

Professor EpwaRD Fawcervr. Journ, of Anat. | : [Puate XVII.

——- Tect. nasi ant.

—--- Sept. int. orb. nas. Prom, frontalis. ..-—--~~ 1 Lam. trans. ant.

- Eth.-turb. I. — Cart. paras. ant.

Comm. sph.-eth. ---~ Fiss. orbito. nasal. —

Ala orbitalis. -— 9 eee ? For. epiopticum. ~-~--For. opt.

-Cart. Meckel. -Ala temp.

-Can, hypophy. For. carotic.

Parietal plate.

Comm. trabec. coch. ant. Comm. trabec. coch. post.

Pars coch. Par. plate.

Fossa subare, ant. int. For. tymp.

Prom. semic. ant. Pars chord. Choraa dors . Prom. semic. ant. .... For. endolym. --—-For. jug.

Can. hypogloss.

~~- Cart. exocc.

Tatusia novemcineta. Chondrocranium of 12-mm. (Wood-Jones) embryo, from above. Lamina transversalis anterior and anterior paraseptal cartilages are procartilaginous. All areas dotted are as yet unchondrified.

Professor EDWARD FAWCETT. Journ. of Anat.]

Sept. nasi.--~ 7/4

Proc. alaris sup. -~—

Lam. trans. ant. ~~ Pars ant. ~ ~ Ductus naso-lacrimalis.

Sule. ant. lat. -—

Cart. parasep, ant. --- Mark Hill (talk) Maxilla. Prom. maxillaris. Maxillo-turb. -Cart. parasep. post. Pars interorb. nas, - Frontale.

Lam, trans. post.

Ala orbitalis, Cupula nasi post.

? For. epiopticum. Ala hypochias.

Fontan. sph. par. Ala temp.

Comm. trabec. coch. ant. Pars cochlearis.


Incus. .

Foramen. tymp. Aud. caps.

For. jug. Can. hypogloss.

Proc. paracondyl



— Incisivum—pars paraseptalis.

Palatinum. Fiss. orb. nasal. For. opticum.

Fiss. trabec. septalis.

Pars trabecularis.

For. caroticum, Chorda dorsalis. Fen. basi-cranialis,

- Nervus facialis, ~ Fiss. basi-coch.

Stapes. Pars chordalis.

Proc. styloideus. Fossa stapedii.

Unchondrified part of auditory caps.

-—---—-. Tect. cranii post.

Tatusia novemeincta. Chondrocranium of 17-mm. (Wood-Jones) embryo, from below.

The lamina transversalis anterior is unchondrified.

Professor EDWARD FAWCETT. Journ. of Anat.} : . (Piate XIX.

| a Hypophysis.

aes Pars trabecularis.

BR ------ Chorda dorsalis.

--- Art. carotid.

-- Chorda dorsalis.

_— Art. staped.

ae nee ene Pars chordalis.

ss eo Nerv. hypog.

Can. hypog.

px- Cart. exocc.

Homo. Chondrocranium of 18°6-mm. (Morgan) embryo, from above.

Professor EDWARD FAWCETT. Journ. of Anat.] {Phare X& OC.

aaaiaaoaae Pituitary body.

=---- Hypophyseal duct. Fars trabecularis,

Caps. auditoria, ------~

Pars chordalis, = Can. hypogloss.

‘ *=-- Chorda dorsalis.

S———=. Dens:

Homo. Chondrocranium of 14-mm. (Barker) embryo, from above.

Professor EDWARD FAWCETT. Journ. of Anat.) [Puare XXI.

Cupula ant.

~ Fenes. narina. ~~ Sule. dorsalis.

-- Nasale.

Cart. parasep. ant. __ ~- Maxillare.

. Pars interorb. nasalis. ~. Frontale. ~ Comm. sph.-eth.

Eth.-turb. I. Tect. nasi post.

--: Fiss. orb. nasal.

Ala orbitalis (radix ant.). Fiss. orb. sup. _. Ala temp. Cart. Meckel. -—— -- For. caroticum.

~ Comm. orb. pariet.

- Pars cochlearis.

Meatus aud. int. Pars chordalis.

Caps. audit, For, endolymph.

~ For. jug.

- Can. hypog].

~- Can. hypogl.

~---+-Tect. cranii post.

Dasyurus viverrinus. Chondrocranium of 9°3-mm. (Hill) embryo, from above.

Professor EDWARD FAWCETT. Journ. of Anat.] [PuatE XXII.

= Mark Hill (talk) Septum nasi.

---" = Pars interorbito-nasalis.

--= Ala orbitalis. 3 --- Eyeball.

== Hypophysis. . ~~" Carotid.

- Trabecula (Pars trabecularis). ~- Medial wall of cochlear capsule chondrified.

“= Cochlear duct.

~- Pars chordalis.

=== Chorda dorsalis.


Talpa. Chondrocranium of 11-mm. embryo, viewed from below.

Cite this page: Hill, M.A. (2021, June 15) Embryology Paper - The primordial cranium of erinaceus europaeus (1918). Retrieved from

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