John Dennison

Patterns of emergence of the human mental nerve

This study investigated the path of emergence of the mental nerve in a number of human population groups. Skeletal material comprised 117 Negro skulls (53 males), 114 caucasoid skulls (62 males) and 100 pre-contact Maori skulls (70 males). In each case, the path of emergence was classified into posterior, anterior, right-angled or multiple. Those cases with severely resorbed alveolar ridges that made classification difficult were excluded from the study. Additionally, 56 cadaveric mandibles were examined, in which an osteotomy of 1cm was made on either side of the mental foramen to expose the nerve. The most common pattern of emergence in caucasoids and Maoris was a posterior direction (86.7% of caucasoid males, 90.2% of caucasoid females; 85.5% of Maori males, 93.1% of Maori females). In Negroes the most common pattern was a right-angled path of emergence (45.8% of males, 45.0% of females), with this difference between population groups being statistically significant (Pearsons chi(2): males=23.4, females=45-97; P<0.01). Multiple foramina were rare, with the highest incidence being in Maori and Negro males. Cadaveric data supported the findings of the skeletal investigation, with the dominant emergence recorded as posteriorly directed (80.7% of males, 86.6% of females). It was concluded that while the traditionally accepted ontogenetic explanation for the inclination of the mental nerve might be applicable to caucasoids and Maoris, it fails to explain the observed right-angled emergence pattern in Negroes. Hence, the nerves emergence might be genetically, rather than functionally, determined. The study did not show a measurable anterior loop in the emergence of the mental nerve that would have any significant impact on treatment planning for implants in the anterior mandible.

More on the Liang Bua finds and modern human cretins

Brown (2012: LB1 and LB6 Homo floresiensis are not modern human (Homo sapiens) cretins, Journal of Human Evolution) makes errors of fact, omission and interpretation. Browns comments refer, among others, to (1) delayed growth and development indicated by unfused epiphyses, (2) postcranial limb proportions: limbs to trunk, between limbs, and within limbs, (3) postcranial bone torsions and angles, (4) postcranial robusticity, real and apparent, (5) skull features, and (6) cretinism on Flores. In each of these areas, much information about cretins is incorrect and much information (Oxnard et al., 2010) comparing the Liang Bua remains with cretins is ignored.

Pathological Anatomy and Histology

In stressing the regularly-present changes in the thyroid gland in our definition of endemic cretinism, we meant not just morphological variation but also a functional deviation from the norm. The latter implies that the organs downstream from the thyroid gland will be drawn into the circle of disruptions as well, and indeed this is expressed not only in a similarly-disturbed function, but also in the form and structural changes in these organs. Not to mention that the thyroid gland to a great extent dominates growth and differentiation of the animal body – through its effect on metabolism it is in a position to influence the morphological side of cells and tissues as well. Whether all these effects can be ascribed to one and the same hormone is still unknown. The thyroxin isolated from the thyroid gland (its chemical formula made known by Harrington’s investigations) might primarily control metabolism and tissue differentiation; however, at a certain dosage, it possesses characteristics for growth. Yet it is quite unlikely that the blood-borne secretion from the active thyroid gland is pure thyroxin, but rather that the thyroxin is present both in the thyroid gland and in its venous drainage, presumably in a bound form (I. Abelin). It will be our task to compare the organ changes occurring in cretinism with the subsequent conditions of definite disturbance in the thyroid gland.

Course and Clinical Pattern of Cretinism

We can obtain an overview of the course of cretinism and its clinical appearance only if we keep its two main anatomical and clinical forms separate – cretinism without goitre and cretinism with goitre. Admittedly, as will be seen in the section on pathological anatomy, the borderline is not sharply defined. For instance, in cretins with early atrophy of the thyroid gland we often find anatomically tiny goitrous nodules that do not attract attention clinically, and, at most, can be palpated only during more detailed examination. In addition, it can happen that early atrophy of the gland’s parenchyma is connected with the development of even bigger isolated nodules. The case must then be assigned anatomically to cretinism with goitre, in spite of its developmental path being that of a cretin without goitre. Such nodules can be intrathoracic and detectable only by x-ray (the case in Fig. 23). Finally, the not uncommon transitions in the clinical picture demonstrate that no sharp border can be drawn temporally and anatomically between early and late atrophy of the thyroid gland. Clinically then, we lock onto early atrophy when, irrespective of the type of intellectual defect, the delay of body growth stands out, and we assume late atrophy when physical development shows a fairly normal tempo during the initial years of schooling. You could object that this is an a priori assumption, but in actual fact it is confirmed by the histological findings in the gland.

Etymology of the Word ‘Cretin’

Until quite recently a kind of uncertainty has predominated as to the origin and original meaning of the word ‘cretin’. It is acknowledged that it emerged only in the eighteenth century, and was mentioned for the first time in the French encyclopaedia of 1754. The word belongs among the dialects of south-eastern France.

Prophylaxis and Treatment of Cretinism

Control of goitre and of cretinism, i.e., endemic thyropathy with its consequences and related phenomena, is today occasionally grouped under the title of racial hygiene. A word of interpretation is essential here. Goitre and cretinism appear in all races wherever the required environmental conditions exist. There is as yet no known race that might be considered secure against endemic thyropathy. Control of the latter is therefore not a question of racial hygiene, but a question of hygiene per se. If you want to define this more precisely, you would have to call it ‘population hygiene’. The misnomer of the label ‘racial hygiene’ crops up particularly in countries inhabited by different ‘races’, such as the Bukowina studied by Flinker. In the Alps, representatives of the Nordic, Alpine and Mediterranean populations all participate in suffering from goitre. The designation ‘racial hygiene’ would have justification in goitre only if you follow Siemens in describing as race the ‘permanent, surviving body of population’.