THE M9TN ANGLE O F CRANIAL FLEXION (THE NASION-PITUITARY-BASTON AXGLF:)

.JOHS CSMERON DidRousie Cnitiersit!y, Balifax. Nova Scotin

CRANIOMETRIC STUDIES, KO. 5

In 1%5( I) the writer piihlished a commuriicatioiz upon this angle, founded upon a study of its anatomy in the American white and the American negro, both iiiale and female. The angle, i t may be noted, is enclosed between lines connecting the pituitary point to the nasion and the basion (fig. 1, p. 332, vol. IX of this journal). Iii the summer of 1926, he was privi- leged to stndy its comparative aiiatomy in the Hamann Museum collection of crania repre sen tin g 1 ower mammalian types.

For the purpose of this investigation, it was essential to hare crania sectioned in the mesial sagittal plane. This a t once created a difficulty, for the writer found that the crania representing the anthropoids and Iower mammalian types in most of the museums where he inquired were usually mounted intact without any sectioning whatever. Fortunately, in the Hamaiin Museum, Western Reserve University, he found crania of all the representative types he required, sectioiied mesially. Some coiisiderable time, ho1xw7cr7 will have to elapse before a sufficient number of mesially sectioned crania is available for the purpose of estimating the average size of the nasioii-pituitary-basion angle in each mammalian type.

In an adult dog (B.49 of the Hamann >Illuscum collection) the angle was found to be 198". T t was thus well above two right angles, this resnlt being, of course, due t o the fact that the pituitary point, instead of being above the nasion-hasion line, m-as actually below it ( fo r example, see fig. 1, p. 130, ~ o l . SIX, Trans. Royal Society of Canada).

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AMERIC4N JOURhAL OF PHYSICAL AXTHROPOLOGY VOL. X, NO 2

276 J O H N CAMERON

In Lemur catta (B. 197 of the Hamam Sluseum collection, which was the cranium of a young adult female) the level of the pituitary point was found to have risen considerably, being in this specimen actually 1 mm. abore the level of the nasion-basion line. This might be described as the evolution- ary sunrise of the pituitary point. The nasion-pituitary- basioii angle was thus estimated to be just under 180°-the actual result being 179". In this marrimaliaii type, therefore, the writer found the first foreshadowing of the cranial flexion that is such a marked feature of the human skull.

As we enter the anthropoid group xTe find some interesting features presented by the nasion-pituitary-basion angle. Fo r example, the gibbon is generally regarded as the most lowly erolved member of this group, aid this was certainly found to be so, as far as this angle was concerned; for the single specimen that was examined (13.549 of the Hamanii Museum collection, which was the skull of an adult male) rieldetl the high figure of 178". That is to say, it exhibited only one more degree of cranial Bexion, as compared with Lemur catta-a yery slight evolutionary adraiice for a genus that qualifies for inclusion in the anthropoid group. A n investigation of the size of tlie angle in the orang (B. 551 of the Hamann Museum collection-a young adult female) and the chimpan- zee (B. 240 of the Hamaiin Museum collection-a young adult female) displayed the fact that decided progress in cranial flexion had taken place, the figures yielded by these two types being 161" and 159", respectively.

The gorilla, which is usually regarded as the most highly cvolvcd member of the anthropoid group, appeared to occupy a somewhat anomalous position, so fa r as this angle was con- cerned, for the result yielded by the only specimen examined (B. 170 of tlie Hamann Nuseum collection-a young adult male) was 178", which was exact17 the same figure as that yielded by the lowly evolved gibbon.

A general survey of the resnlts obtained in the anthropoid group brings out two facts very clearly. In the first place, it is evident tliat the influence of sex upon the size of the nasion-

CRANIOMETBIC S T U D I E S 277

pituitary-basion angle will have to be investigated in all these lox-er mammalian types whenever a sufficient numlser of crania becomes available for study. This is essential, since the writer(1) has already pointed out that the angle is con- sistently greater in the female American white aiid the female American negro than in the corresponding males. In the sec- ond place, the range of variation in the four members of the anthropoid group, both males and females, will require close investigation, as tlie results yielded hy the single gorilla speci- men suggest that this range is very extensive, just as in tlie Hominida e.

TABLE 1

To show that there as a giaduat aizd progresszve dwnznutioib t i 2 t h e szze of the ii,azn, angle or rraiizal flexion as we a s c e d through lower ?naiiimals, the arkthropoids, cmd the qtegro race, right u p t o the higher Tares of the Honmidas

Dog7 Lemur, Gibbon, Gorilla, Orang,

198" Chimpanzee, 159" l i Y O Female American iiegro, 137" 178" Male American negro, 135" 178" Female American white, 134" 161" Male American white, 131.5"

An examination of table 1 shows that a vast evolutionary gap exists betiveen the anthropoids and man. Thus the size of the angle in the female American iiegro will be observed to be twenty-two degrees less than in the nearest anthropoid, namely, the chimpanzee. This is logically the space where the various 'missing links' would have to fit in. The writer woiild therefore be most kceii to find out the size of the angle in the recently (September, 1926) discovered cranium of Pi thecan tliropus erectus, wliich, according to tlie latest re- ports, appears to be in a good state of preservation.

A study of the range of variation of the nasion-pituitary- basion angle in the Hominidae, however, disclosed the inter- esting fact that its masimnm approximated to the dimelisions fouiid among the anthropoids. For example, the high figure of 162.5" found in male iiegro cranium no. 662 was greater than that fouiid in the orang and the chimpanzee. The high maximum of 158.5" yielded by female negro cranium no. 545

278 JOHN C,A&fERON

likewise closely approached these two anthropoid types. Tlie maxima found in the male and female wliiie material even rose to 150" or more. For instance, male white cranium no. 628 yielded a nasion-pituitary-basion angle of 153", while in female white cranium no. 675 it measured 150". These facts are all fully illustrated i n table 2.

TABLE 2

To show that the maximum sizes of the main angle of cranial flexion in the

that the neyro types showed higher maxima tlkan the whites Horninidae muy approximcate to those f o u n d in the anthropoids. Note

Gibbon, 178" Maximum size in female Amer-

Maximum size in male Ameri- Maximum size in male Ameri- Gorilla, 178" ican negro, 158.,5

Can negro, 162.5" can white, 153" Orang, Chimpanzee,

161" Maximum size in female Amer- 159" ican white, 150"

A reference to the writer's recent paper(1) on the nasion- pituitary-basion angle will &ow that he chose it as an index of cranial flexion in preference to the spheiio-ethmoidal angle devised by Huxley (2). The salient of the spheno-ethmoidal angle, namely, the prosphenion, is nearer to the nasion than the pituitary point. The result is that the spheno-ethmoidal angle will always register a higher figure than the iiasion- pituitary-basion angle in the same mammalian type. This will be found to be so on comparing Duckworth's list of measurements of the spheno-ethmoidal angle (3) with those of the nasion-pituitary-basion aiigle in table 1. For example, he found the spheno-ethmoidal angle in the dog to be 231", which is thirty-three degrees greater than the nasion- pituitary-basion angle in this type. The same observer gives 202" as the numerical value of the spheno-ethmoidal angle in the orang, which is forty-one degrees greater than the nasion- pituitary-basion angle in this anthropoid. Again, the spheno- ethmoidal angle in the chimpanzee is given as 168" in Duckworth's table, which is nine degrees greater than the nasion-pituitary-basion angle, as found by the writer in this anthropoid.

C R A N I O M E T R I C S T U D I E S 279

The cornparisoil between these two angles in the gorilla is surprising. Thus Duckworth found the spheno-ethmoidal angle in this aiithropoid type 158", which is actually twenty degrees less than the iiasion-pituitai-y-ha~ion angle. This anomaly adds further emphasis to the remarks made by the writer earlier in this paper, namely, that all these cranial angles mill be found to exhibit very wide ranges of variation in lower mammalian types, just as in man.

On coming now to the Hominidae, it may be noted that the spheno-ethmoidal angle is given by Duckw-orth as 153" in the aboriginal Australiaii (average of two) and as 138" in the European (average of two). As was to be expected, these are higher than the average figures f o r the nasion-pituitary- basion angle in the male American white (131.5") and in the female American white (134."), as ascertained by the writer (1).

SUMMART

1. The main angle of cranial flexion reaches its minimum size in tlic x4iite races of mankind.

2. It exhibits a gradual and progressive increase i n size as we descend the mammalian scale.

3. This angle is an index of the gradual flexion which the basis cranii undergoes as we ascend the mammalian scale, finally culminating ia the white races. 4. The first foreshadowings of this cranial flexion are found

in the lemurs. 5. A study of the angle in the anthropoids suggests that

it possesses wide ranges of variation, as in man. 6. It is eTrident that there is likewise a sexual factor which

determines the size of the angle. 7. A rast evolutionary gap exists between the anthropoids

and man, with regard to the size of this angle. This is logi- cally the space where the x-arious 'missing links' would have to fit in.

LITERATURE CITED

I CAMERON, JOHN 19% Thr eranio facial axis of Huxley, pt. 11. Tr. Roy.

2 IITJXLEY, T. H. 1864 Lectures on comparative anatomy. London. 3 DUCKWORTH, W. L. 13. 1904 Morpliology and anthropology. Cambridge.

Xoc. Can., third series, XIX.